Fabregas to miss Old Trafford trip
The Spanish midfielder tweaked a hamstring injury during Tuesday's Champions League defeat in Barcelona.
"He will be out maybe for the next two games," Wenger told a news conference.
Goalkeeper Wojciech Szczesny suffered a finger injury against Barcelona and will also miss the game at Old Trafford on Saturday.
"He is out for a while," Wenger said.
Striker Robin van Persie, controversially sent off against Barcelona, will be available for the United match and Wenger said he would play his strongest team.
"We can take confidence and belief from the Barcelona tie," said Wenger whose team lost 3-1 at the Nou Camp after winning the home leg 2-1.
Arsenal, three points behind leaders United in the Premier League with a game in hand, lost to Birmingham City in the League Cup final two weeks ago and the defeat by Barcelona leaves them with only two chances to end a six-year trophy drought.