AC Milan's Antonio Cassano reacts during their Italian Serie A soccer match against Juventus at the Juventus Stadium in Turin Oct 2, 2011. [Photo/Agencies]

AC Milan and Italy forward Antonio Cassano has been struck down with an undiagnosed illness and is undergoing tests in hospital, the club said on Sunday.

Cassano seems likely to miss the trip to Belarus for Tuesday's Champions League Group H game against BATE Borisov.

"Antonio Cassano was taken ill last night on the arrival of the flight from Rome," Milan, who won 3-2 at AS Roma in Serie A on Saturday, said in a statement.

"The player was taken to Milan's Policlinico hospital for checks."

Media reports in Italy said Cassano, who helped Milan win last term's scudetto, could hardly talk or move.