Jackie McNamara has a full squad to choose from in his first game as Dundee United manager.
United kept their squad intact on transfer deadline day despite reported interest in forward Johnny Russell.
Czech midfielder Rudi Skacel's short-term contract expired on Wednesday.
Rangers striker Francisco Sandaza is rated doubtful.
The Spaniard is struggling with a hamstring problem, while skipper Lee McCulloch has failed to recover from an ankle injury in time.
Lewis Macleod also misses the clash at Tannadice after being ruled out for seven weeks with knee ligament damage sustained against Montrose last weekend.
Williams is pushing for his first start when the Shrimps travel to York after two scoring cameos from the bench, including last weekend's dramatic late winner against Dagenham.
The midfielder has trained with Morecambe since the summer but clearance issues prevented him from signing professional terms until earlier this month.
"He's had a massive impact," Roche said. "He's been with us really since the start of pre-season and he's come in each day working his socks off knowing that he wasn't going to be able to get a deal until maybe January.
"So he's been coming in off his own back not getting paid and he's worked really, really hard.
"Given the chance when he's got it he's taken it and been absolutely brilliant. He's scored two very good goals but also Saturday's goal was so important to our season."
The Canaries head to bottom club QPR on Saturday some seven points clear of the drop zone, but without a league win since December 15.
Argentinian forward Becchio - who scored 19 goals for Leeds this season and arrived as part of a swap deal for Wales international Steve Morison - will provide much-needed back-up for captain Grant Holt, and could well be used as an impact player from the bench on Saturday.
"Becchio is a player in good form this season, which is important," Hughton told a press conference.
"You want someone who is going to hit the ground running and give us something, whether it is starting or on the bench."
Norwich also moved to bring in Kei Kamara on loan from Major League Soccer club Sporting Kansas City, but the Sierra Leone forward is still waiting for international clearance and will not feature this weekend.
Hughton confirmed the Canaries had tabled several "substantial bids" for Celtic frontman Gary Hooper, all of which were rebuffed by the Scottish Premier League side, who are said to have last night slapped a ?10million price-tag on their prized-asset.
"We did put bids in and they were substantial bids, certainly by the levels of this football club," said Hughton.
"All the conversations we had with Celtic were good, amicable conversations, but it was very clear he is a player who they had a big valuation of and did not want to lose."
QPR, meanwhile, broke their transfer record to bring in former Blackburn centre-back Christopher Samba having already splashed out some ?8million for striker Loic Remy earlier in the window.
Should Harry Redknapp's men somehow manage to avoid relegation, it would be money well spent.
Norwich head to Loftus Road on the back of a 1-1 draw with Tottenham, which went some way to restoring confidence after the 5-0 mauling at Liverpool had made it five defeats from six Premier League games.
Hughton knows Norwich must be on their guard tomorrow.
"QPR are in good form and are confident, they have brought in some very good quality players," he said.
"They had an effective system up against Manchester City.
"Whether they see this as a home game which is winnable, perhaps their tactics will be a bit different.
"Every three points for us are valuable, which is the same for QPR.
"We need to go into the game with the same spirit and determination as we had against Spurs."
Despite Norwich's alarming slump, Hughton remains confident they can recapture the consistency which saw his side recover from an appalling start to the season and embark upon an 11-game unbeaten league run which included wins over Arsenal and Manchester United.
"We know where we are - it is difficult for us to sustain the form we showed a few months ago right the way through the season, so you are going to have you lows, you have to accept it and it is how you respond," he said.
"It was a performance against Spurs like which we had showed before the dip, so that is encouraging.
"We just need to pick up points where we can now, with strong performances in every game."
England keeper John Ruddy continues his rehabilitation from a thigh operation, and Hughton maintained the Canaries number one must not be rushed back into action.
He said: "John is on track and is in very good shape, but it is one which has to take its course.
"Of course you would like to have him back as quickly as possible, but we have to react to what is good medical advice and make sure his rehab is exactly how it should be."
The William Hill Scottish Cup tie is set to be played in controversial and unusual circumstances after Rangers opted against taking a ticket allocation for the visit to Tannadice.
The club took the decision after fans' groups called for a boycott of what will be the first away match against Clydesdale Bank Premier League opposition since the Light Blues were denied entry to the top flight after being consigned to liquidation in the summer.
Around 10,000 home fans are expected to watch Jackie McNamara's debut as United boss, with only a few hundred away supporters expected on Tayside.
McCoist, who hopes the situation is a one-off, said: "There has been a lot of stuff written and a lot of stuff said. I think now is the time to actually take the sting out of the whole situation to be honest.
"Jackie is a great lad. I wished him all the best in his job and we'll shake hands before the game.
"All it is, is a cup tie that both teams want to win. It's going to be a little bit different because the club have taken the stance not to take any tickets for the game.
"That stance has been made and hopefully it's just a one-off and we can move on. People are probably reading a lot more into it and wanting to build a lot more out of it than they should.
"It's a cup game that's important to both clubs and both clubs want to win. It's no more than that.
"I do appreciate there will be an edge to the game but we all have a duty and a responsibility to do our best for our clubs and, indeed, behave ourselves.
"That will hopefully be the case."
McCoist has praised fans on many occasions this season for the impressive backing they have shown to Rangers in the Irn-Bru Third Division.
He admits a lack of support against United will make the task tougher, but believes his side can still triumph in the fifth-round tie.
He said: "It's not an ideal situation, of course it's not. We would rather take what is a tremendous away support.
"If they followed us to Elgin, Berwick, Peterhead and Forres, I think there is every chance they would have followed us to Dundee as well.
"But circumstances have dictated that we haven't taken a ticket allocation.
"It's not ideal and it will make it more difficult. That said, I've played in away games myself where we haven't taken any support which has worked out reasonably well for us.
"I'm keeping my fingers crossed that will be the case (on Saturday)."
McCoist refused to be critical of Rangers fans who do make the trip to Tannadice.
He added: "We've taken a stance on it and we've already made our views clear on it, that we didn't take any tickets.
"It was all or nothing for me, that's my opinion.
"But we've got such a great support and I can understand that they want to travel all over the world to watch us, and they're proud of the fact that they don't miss any games.
"So I can understand the fans' disappointment and I can understand some fans wanting to go.
"I would imagine some fans will be there and I can totally accept that."
On the match itself, McCoist said: "I'm not attempting to play mind games.
"Dundee United will be favourites, they must be favourites.
"I think the bookies would tell you that and it's not often the bookies get it wrong.
"The best way to put it is, at the start of the season - outside Celtic - Dundee United would have been many people's favourites to win the cup.
"I understand Jackie's views - he's not going to treat us lightly and I didn't think for a minute that he would.
"But Dundee United will start the game as firm favourites."
A transfer embargo meant McCoist was unable to make use of the January transfer window, but is continuing his search for players he can recruit on pre-contract agreements before registering them as free agents in September.
He said: "We've certainly had positives in terms of one or two players who we would like to come, who are out of contract and we can register in September."
