Arsenal full-back Hector Bellerin has had to visit hospital for tests on a knee ligament injury, manager Arsene Wenger has confirmed.
The Spain international had played every minute of the Gunners' Premier League campaign until he was not included in the starting line-up for Sunday's 2-1 Premier League defeat to Brighton and Hove Albion.
"No, he is injured," Wenger told a news conference when asked if Bellerin would feature at San Siro on Thursday.
"He has an inflammation of his left knee. Some ligament damage. He had to spend the afternoon in the hospital to see why he is in so much pain.
"It's not a long-term thing."
Arsenal will also be without Nacho Monreal and Alexandre Lacazette against Milan, although they have no other injury worries.
"For team news, apart from that, of course Lacazette is not ready and we had to leave Monreal behind as well because he's not ready," said Wenger.
"He started a little session but he's not ready."
2520 - Hector Bellerin was the only player to have played every minute of Premier League action for Arsenal this season, prior to today's game. Rested. pic.twitter.com/YEhHciLkI1— OptaJoe (@OptaJoe) March 4, 2018
Arsenal are looking to end a run of four consecutive defeats in all competitions, their worst sequence since October 2002.