BBC Sport - Arsenal fear Bukayo Saka could miss a minimum of six weeks with the quadriceps injury he sustained in their Champions League tie against Bayern Munich.
The 25-year-old will undergo an MRI scan on Friday afternoon to better assess the problem, which forced him off in Wednesday's 2-2 draw at the Allianz Arena.
Fluid around the affected muscle has made diagnosing the injury difficult, but club medics are estimating, after early examinations, Saka will miss a minimum of six weeks and it could be even longer.
If those early concerns are realised, he will miss a clutch of key games for the Gunners, as well as England's forthcoming Uefa Nations League matches against Croatia and Spain.
"We need a few more scans and opinions from the specialists," said Arsenal head coach Mikel Arteta.
"When a player has to walk off the pitch, he is struggling to walk without any pain, and is restricted to movement; it is not a good sign. Let's be a little bit patient so we can give a definitive assessment.
"He's got another MRI as there was quite a lot of fluid in the area so it was quite difficult to understand the extent of the injury. We will know more tomorrow."
Saka will miss Saturday's home Premier League match against Everton, where second-placed Arsenal will hope to close a three-point gap on leaders Manchester City.
The Arsenal academy product has had fitness issues in recent months and his game time was managed at the end of last season, as well as with England at the World Cup, because of an Achilles injury he suffered in March.
He missed the March international break and seven games for the Gunners, but returned to help them lift the Premier League title for the first time in 22 years.
Saka started the Champions League final defeat by Paris St-Germain but was substituted after 54 minutes, and only started three of England's eight games at the World Cup - scoring a hat-trick in the 6-4 third-place win over France.
The forward also had surgery on a hamstring injury he picked up in December 2024, which kept him out for 101 days in the 2024-25 campaign.
He made 49 appearances as Arsenal won the title last term, despite a stop-start season. As well as the Achilles issue, Saka pulled out of a game in January against Leeds with a hip injury in the warm-up, while a hamstring problem also kept him out for about four weeks.