Arsenal boss Unai Emery says goalkeeper Petr Cech could be sidelined for up to three weeks after limping off during the win over Watford.
Cech suffered an injury in the first half of the 2-0 win at the Emirates Stadium and had to be replaced by Bernd Leno.
And the 36-year-old Cech will be assessed by the Arsenal medical team on Sunday.
Emery said after the match: "I think it's a hamstring.
"Maybe he will miss two or three weeks. I hope not more.
"We will see tomorrow."
Leno performed well after coming off the bench for his first taste of Premier League action since arriving in the summer from Bayer Leverkusen.
Watford created several opportunities after the break but Leno denied the visitors with some good saves.
"I'm very happy with Leno," said Emery.
"I think he was content to wait for this moment and now it is arriving.
"His performance was the best for us today."