Arsenal boss Arsene Wenger fears striker Alexandre Lacazette could be "out for a while" after suffering a suspected groin injury in Wednesday's 5-0 win against Huddersfield.
Lacazette, 26, scored the opener but was replaced at half-time by Oliver Giroud.
The France international has scored seven goals for the Gunners since joining from Lyon in July for £46.5m.
"He's definitely out for [Manchester United] this weekend," said Wenger.
"It looked like a groin injury. He could be out for a while."