Ilkay Gundogan could face a month on the sidelines after his return to the Manchester City starting line-up in Wednesday's 2-1 EFL Cup win at West Brom ended prematurely due to another knee injury setback.
The Germany international midfielder tore his right anterior cruciate ligament against Watford last December but came on as a substitute in a 6-0 win against the same opponents on Saturday.
Pep Guardiola named Gundogan in his XI at The Hawthorns and he was instrumental in a dominant first-half showing, although the visitors were unable to add to Leroy Sane's third-minute opener before the break.
That goal arrived after Ben Foster saved from Gundogan, who was cut down at the end of a driving 54th-minute run by Claudio Yacob and was unable to continue.
Yacob equalised to reward a much-improved West Brom display in the second period, although Sane settled matters with a fine 77th-minute winner.
Speaking at a post-match news conference, Guardiola attempted to allay fears of a further serious setback for Gundogan, who missed Euro 2016 with a dislocated kneecap.
"I think it's not serious. Maybe a month out," he said.
"Unfortunately the action [tackle] was tough. He will back soon, hopefully.
"He's okay. I spoke with him, he has a little pain in his knee. Tomorrow the doctor will clarify but it doesn't look serious."
Job done tonight pic.twitter.com/iBxN0u6aYF-- Manchester City (@ManCity) September 20, 2017
West Brom boss Tony Pulis defended Yacob when asked about his player's challenge.
"I've been told Yacob got the ball," he said. "The lad [Gundogan] looked okay walking off.
"City got their free-kick, Yacob got booked."
City will host Championship side Wolves in the fourth round next month.
"We will respect Wolves and we know from our experience against Huddersfield last season [it will be difficult] so we will be ready," Guardiola added, his team having been taken to a replay in the fifth round of the FA Cup by the then-Championship Terriers.