Welbeck was caught by a nasty challenge from Nigel de Jong in the second-half, which sparked a furious touchline row between Sir Alex Ferguson and Roberto Mancini. It is not known whether he sustained the injury in that incident.
However, if the damage is bad, it could have serious consequences for Roy Hodgson, who seemed likely to select Welbeck in his European Championship squad if, as expected, he is confirmed as Fabio Capello's replacement.
Ferguson was certainly not happy with De Jong's challenge, nor the manner in which Mancini was talking to fourth official Mike Jones.
Jones stood between the pair at one point during the row to prevent it spilling over before they were eventually pulled apart by members of their respective backroom teams.