Rooney was initially expected to be out for just two weeks following the injury sustained in a 1-1 result with Swansea City on Dec. 23. However, United boss Sir Alex Ferguson has said that there has been a frustrating delay in the England international’s return.
"Wayne's still injured, and it looks like going to be out another two weeks or so," Sir Alex Ferguson said, according to Manchester United’s official Web site.
"It's a surprise as he was meant to be back training now. So he'll be out for longer than we thought and I don't think he will be fit for the Liverpool match. The injury is nothing serious. He just got clipped behind his knee. Nothing shows in the scan but he's still feeling it. Hopefully in two weeks it'll be sorted but nonetheless it's a loss."
Rooney has already missed a month of action earlier in the season following a nasty leg gash suffered in United’s second match of the campaign against Everton.
The 27-year-old has scored eight goals and contributed nine assists in 19 appearances for United.