AC Milan striker Antonio Cassano will have minor heart surgery and is expected to be able to play again in a few months, the Italian club has said.
The striker, 29, has been in hospital since being taken ill following the 3-2 win over Roma in Serie A on Saturday.
He had vision problems on a plane journey and Italian news agency Ansa initially claimed he suffered a stroke.
Coach Massimiliano Allegri said his team were "playing for Cassano" in the Champions League on Tuesday.
The Italian giants drew 1-1 with BATE Borisov in Belarussia and lie second to Barcelona in Group H.
Before the game, Allegri said: "We will be playing for Antonio. Quite apart from the sporting element, what counts most is the human aspect and we're all feeling sad.
"Antonio was doing well and he was in good shape and I hope he'll be back as soon as possible.
"I can't diagnose him but he sounds fine. It was completely unexpected and has nothing to do with football. Let's leave it to the doctors and I think everything will be fine."
Cassano had reportedly developed problems with vision, speech and movement on the plane and had tests on his heart and brain in hospital.
CASSANO'S CLUBS
Bari (1999-2001) 48 league games, six goals
Roma (2001-06) 118 games, 39 goals
Real Madrid (2006-08) 19 games, two goals
Sampdoria (loan 2007-08) 22 games, 10 goals
Sampdoria (2008-11) 96 games, 35 goals
AC Milan (2011-) 26 games, eight goals
