AC Milan's Champions League hopes have suffered a major blow after top scorer Alexandre Pato limped out of Sunday's league win over Atalanta.
The Brazil star set Milan on course for a 3-1 win with a first-half double at the San Siro but pulled up late on while in full flow, clutching his thigh.
The 20-year-old looked distraught as he headed for the dressing rooms and it was feared he had suffered a recurrence of the adductor injury that recently kept him out for two months.
Pato has only played five games since returning from injury, which included the 3-2 defeat by Manchester United in the first leg of their Champions League knock-out tie.
The Italian giants now face an anxious wait to see if Pato will be fit in time for the second leg at Old Trafford on 10th March.
"We will have to wait 24 to 48 hours before knowing the extent of the injury," said Milan vice-president Adriano Galliani.
"Not to have Pato would be terrible. We don't have anyone who can replace him. Without him, we would need to change our tactical set-up."
Pato has been in superb form this season, with Sunday's brace taking his league tally to 12 goals from 17 starts, and he has scored two goals in seven Champions League games.
"We have to see what type of injury he's suffered but it's true that his last injury was to an adductor so that is a little worry," coach Leonardo told Sky Italia.
"It doesn't seem as bad as it seemed on the pitch but it still worries us."
Pato is also hoping to lead Brazil's challenge at this summer's World Cup in South Africa.