Arsenal midfielder Alex Oxlade-Chamberlain will be out for a "few weeks" with a knee injury, says manager Arsene Wenger.
The 22-year-old England international suffered the knock in a challenge with Barcelona's Javier Mascherano during Tuesday's Champions League last-16 tie.
He left Emirates Stadium on crutches after the 2-0 first-leg defeat.
"We lost Chamberlain on Tuesday. His injury is quite serious and keeps him out for a few weeks," said Wenger.
The French manager added that could mean "two or three weeks" or perhaps "six or seven" depending on the verdict of a specialist.
Oxlade-Chamberlain joins three other Arsenal midfielders on the sidelines - Tomas Rosicky, Jack Wilshere and Santi Cazorla.