Arsenal will be without their Spanish right-back Hector Bellerin for four weeks due to an ankle injury, manager Arsene Wenger revealed on Thursday.
The Spain international, 21, sustained the injury during the latter stages of Arsenal's 1-1 draw with Tottenham Hotspur prior to the international break.
Rose challenge "very strong"
"Hector is out for four weeks," Wenger told a press conference ahead of Saturday's trip to Manchester United. "He got injured in the last 10 seconds against Spurs after a very strong tackle by Danny Rose."
Bellerin's compatriot Santi Cazorla remains sidelined with an Achilles problem that has kept the midfielder out of action since last month's 6-0 Champions League win over Ludogorets Razgrad.
Sanchez in balance for Old Trafford trip
Wenger plans to check on Alexis Sanchez's fitness before deciding whether the Chilean forward is in a position to start the game at Old Trafford.
Sanchez scored twice for Chile in a 3-1 World Cup qualifying win over Uruguay on Tuesday, despite Wenger warning beforehand it would be "suicidal" for him to play due to a hamstring problem.
The 27-year-old is not due to return to Arsenal's London Colney training base until Friday.
"I haven't heard a lot (about Sanchez) because we were in doubt 24 hours before the game against Uruguay," Wenger said.
"We didn't know if he'd play or not. In the end they decided to play him. He texted us to tell us he's in good shape after the game.
United v Arsenal
"He came off after 84 minutes and now we have to wait. I see him tomorrow morning and then I will see if he can be involved in the squad or not."
Arsenal are fourth in the Premier League table and will provisionally go top if they beat United in Saturday's early kick-off.