The England captain was left out of the Red Devils’ squad for the first leg of their Europa League last 32 clash with FC Midtjylland amid fitness fears.
And now reports claim that he could miss as much as two month of action due to knee ligament damage.
The news will come as a huge blow for under-fire manager Louis van Gaal, with his side clinging on to hopes of a top four finish.
United currently trail fourth place Manchester City by six points, and with Rooney the only orthodox centre-forward available to LVG, the club’s goalscoring threat is likely to be heavily reduced.
The 30-year-old could miss big matches against Arsenal and Man City, with a mid-April return on the cards – this will leave him with only a handful of games before the close of the season.
Rooney has been in excellent form since the start of 2016, netting seven goals in nine games.