Initial tests on the 29-year-old’s knee were inconclusive but medical staff at Man United fear he could be sidelined for up to a month if the worst-case scenario is borne out.
However, the club remain hopeful that the injury isn’t that serious and Rooney will recover in time to line up in the final few games of the campaign.
The news will come as a blow to Louis van Gaal given that Rooney had become his focal man up front but the return of Robin van Persie will offer him some comfort.
Van Persie, who is continuing his recovery from an ankle injury, scored twice in the 4-1 victory against Fulham for United U21s on Tuesday.
The other alternative for van Gaal, Radamel Falcao, has been poor for the majority of the season so van Persie’s return to goalscoring form couldn’t come at a better time.