Tottenham midfielder Sandro has undergone a knee operation.
The Brazil international was injured during the first half of Spurs' weekend draw at QPR.
And a short statement on the club's website confirmed surgery was required to repair an unspecified problem.
It read: "Sandro has undergone knee surgery following the injury that forced his substitution against QPR at the weekend. The midfielder's recovery schedule will be assessed over the next few days."
Sandro later wrote on his Twitter page: "My surgery went well, now its moving forwards with treatment and rest. Many thanks to everyone for their support - I'll be fine to fight again."
Andre Villas-Boas suggested in the immediate aftermath of Saturday's game that Sandro's injury was not serious.
He said at the time: "He should be okay for the Manchester United game next week. It's just a knock on the knee."
The Huddersfield striker agreed a three-month loan deal last week, but the Reds will wait a further seven days so he will be eligible for the rest of the campaign.
Spencer will therefore miss the game against Carlisle on Saturday but should be available for the trip to Sheffield United on January 26 if the 21-year-old overcomes his current knee injury.
Boss Richie Barker told the Crawley Observer: "We've put it back a week so that it ends on the final day of the season.
"We wouldn't half have egg on our faces if we find he has a lot of goals and we get to the last day of the season needing something and he's not available."
Barker also confirmed he has fielded "an enquiry" about striker John Akinde, currently out of favour at Broadfield after making just 10 appearances this term.
Fenlon has not featured for the Dons for over a month and will see opportunities for inclusion in Neal Ardley's first team further limited by the signing of Hussey.
The teenager is hoping to add to the 18 appearances he has already made for the League Two club this season, but says he is willing to be patient and learn from his more experienced team-mates.
He told the Hounslow Chronicle: "I'm young and he [Neal Ardley] has said I will get my chance. He told me to train well and whenever I get my chance to just take it.
"We haven't spoken about [a possible loan move] so we'll see what happens in the future.
"I can learn from Chris and it's good to have experienced players around me. He's come from a higher level and obviously I'm looking to make myself a better player by picking things up from him."
The decision to rule that referee Mike Dean had made an error was the latest in a rash of judgements this season which has seen the Football Association's regulatory commission overturn no fewer than six red cards handed out to top-flight players.
Kompany was sent off for a two-footed tackle on Arsenal's Jack Wilshere and the FA's decision has been privately condemned by some officials.
Elleray is chairman of the FA's referees committee and, speaking at the launch of the organisation's 150th anniversary celebrations, he insisted officials would not be suffering any crisis of confidence as a result.
He said: "The FA has an independent regulatory decision and it has to decide if they believe a referee made a clear and obvious error, and in their view he (Dean) did.
"When you have a referee's decision overturned then some people will be disappointed but ultimately there's a process which has to be gone through.
"We always say to referees to do their job on the field of play and not to worry about anything that happens afterwards.
"Football's history is full of disciplinary decisions that have been overturned but referees are not being influenced by decisions by the regulatory commissions.
"I think there is disappointment in the decision by referees but they accept there is an off-the-field process and there are also certain occasions where clubs, players and managers are disappointed when red cards are supported."
Elleray said some decisions were judgement calls which were extremely difficult to make in a split second but that is "the beauty" of the game.
He added: "The issue is that there will always be some incidents in football which are not black and white. And if you step back that's the beauty of football because people then have things to discuss.
"You have to remember the referee makes an honest decision in real time and they won't get the decision right all the time.
"If you look at the second Manchester United goal on Sunday, if you slow it down there's a case for offside but it would be impossible for anyone to see that in real time. Referees make judgements in a split second."
Apart from Kompany, the other players to have red cards overturned this season were Carlton Cole and Darron Gibson in last month's game between West Ham and Everton, Stoke's Steven Nzonzi, Jordi Gomez of Wigan and Tom Huddlestone of Tottenham.
The Alex play host to promotion hopefuls MK Dons at Gresty Road this weekend, aiming to close in on the top six.
Ellis, who could return to the starting line-up for the visit of the Dons after missing Tuesday's 4-1 win over Bradford, believes the Railwaymen can push on in the second half of the season.
He told the club's official website: "We have a good enough team to really push on. We just have to keep battling away and keep on winning games. The manager wants to manage at the highest level he can. He wants to push on in his career with us and we want to be there.
"We are three points off the play-offs. We have a good set of players who want to work hard for the club.
"I set myself a target of playing every league game and I have done that so far, so I hope to keep that up and get a few more goals as well."
