Ruben Loftus-Cheek will miss AC Milan's Serie A clash at Napoli on Sunday after being rushed to hospital to have his appendix removed.
In a statement, Milan said that Loftus-Cheek felt "serious abdominal pain" during his team's training retreat ahead of the match in Naples.
"Tests revealed acute appendicitis. Ruben will undergo surgery today to have his appendix taken out," added Milan.
Loftus-Cheek, 29, has suffered a series of injuries this season, playing only 22 times in all competitions for the seven-time European champions.
Milan sit ninth in Serie A, nine points from the Champions League positions after fourth-placed Bologna won 1-0 at Venezia on Saturday.