Arsenal full-back Hector Bellerín 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.
Wenger said on Wednesday that Bellerín will not return for the first leg of the Europa League last-16 tie with AC Milan, although he does not fear the problem is long term.
"No, he is injured," Wenger told a news conference when asked if Bellerín 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."
Arsenal are looking to end a run of four consecutive defeats in all competitions, their worst sequence since October 2002.