London - Arsenal midfielder Aaron Ramsey will be out for three weeks after sustaining a calf strain during his side's 2-1 loss to Watford, manager Arsene Wenger revealed on Friday.
"Overall from the other night we lose Aaron Ramsey," Wenger told his weekly press conference at the Arsenal training ground in London Colney, north of London.
"He is expected to be out for 21 days. We are a bit short at the moment, but we have young players who can do well."
Ramsey, 26, spent 10 weeks on the sidelines with a hamstring injury earlier this season.
The Wales international's absence leaves Arsenal short in central midfield ahead of Saturday's trip to Premier League leaders Chelsea.
Granit Xhaka is banned, Santi Cazorla remains injured and Mohamed Elneny is preparing for the Africa Cup of Nations final with Egypt in Gabon.
Jack Wilshere, meanwhile, is still on loan at Bournemouth, but Wenger said he had no regrets about allowing the England international to leave on a season-long deal.
Asked if it would be helpful if Wilshere was available to him, Wenger replied: "Well, yes, but I would like to reiterate he wanted to go out and play.
"There is a huge level of competition and we accepted to let him go, so we have to deal with the consequences."
Arsenal trail Chelsea by nine points and sit in third place, below Tottenham Hotspur on goal difference.