Arsenal manager Arsene Wenger confirmed in his prematch press conference that midfielder Francis Coquelin will miss about three weeks after suffering a knee injury in a 3-0 win against Chelsea at the Emirates on Saturday.
"He is out for the game tomorrow," Wenger told the club website, "but it should be a short-term injury because the scan was quite positive and I think it will be three weeks out.
"It’s positive because last year during this period we got some bad news and a few long-term injuries and it was a handicap in our season."
The 25-year-old missed two months last season with a similar injury in the same knee, but has started five of the club's five Premier League matches this season.