Valencia has endured a difficult start to the campaign, missing the entire pre-season and the first month of competitive action after suffering an ankle injury during Copa America.
The winger then ended up playing right-back to cover for Manchester United's defensive injury problems.
However, ahead of Sunday's crucial trip to Arsenal, the 26-year-old is hitting the mark again.
And Rooney is delighted.
"Antonio has been playing brilliantly," said the United striker.
"He is back to his best and when he is like that he is so difficult to defend against.
"It is great for the forwards because he is so good at delivering the ball into the box quickly."
Valencia's contribution helped United make a speedy return to winning ways after their unexpected setbacks against Blackburn and Newcastle over Christmas.
Before that, the Red Devils had been breathing heavily down the necks of leaders Manchester City after recovering from the 6-1 derby defeat by taking 25 points from a possible 27.
They are now in the tricky position of playing catch-up, right at the start of a run of fixtures that sees them tackle four major rivals in their next six league games, in addition to next weekend's FA Cup fourth round clash with Liverpool.
Even Sir Alex Ferguson concedes it will be the period that will define United's season.
And Rooney is just glad the Red Devils have thrown off the mid-season shackles attached to prevent a repeat of their derby debacle.
"The chances are coming again now," he said.
"Those games when we were winning 1-0 were really important. We had to defend and be solid as a team.
"Now we are starting to score a few more goals again."
Injuries are starting to ease too.
Chris Smalling and Phil Jones are due to return for the Arsenal encounter, whilst Tom Cleverley and Ashley Young should be back in a matter of weeks from their long-term problems.
The returns are being welcomed, as is news of a potential bid for Crystal Palace's England Under-21 full-back Nathanial Clyne, who is out of contract in the summer, because Nemanja Vidic and Darren Fletcher have both been ruled out for the season.
But Smalling concedes the constant changing has been disruptive.
"Nobody could have foreseen all the injuries we have had," said the England defender.
"At the start of the season we had good numbers and good quality.
"With so many injuries, the form was bound to dip once or twice. But we are all pulling together and there have been plenty of good results."
It is the bad ones that attract the attention though.
Should United suffer their fourth defeat of the season this weekend and find themselves six points adrift of Manchester City, who take on Tottenham a couple of hours earlier, the critics will be out again.
Such criticism is a new experience for Smalling, who won a Premier League winners' medal in his first season with the Old Trafford outfit.
However, he understands the demands of playing for such a huge club and the reaction that comes with failure.
"I can understand the criticism because we are behind City in the league, and the expectations of this club - from both inside and out - are massive," he said.
"If we are not on top, everyone is asking why, and rightly so.
"Finishing second with more points that we collected last season won't make us feel any better about ourselves.
"The only objective is to win the league."
