Chelsea manager Graham Potter says Reece James will see a specialist to determine the full extent of the defender’s knee injury.
The England right-back, 22, limped off during the Blues’ 2-0 victory over AC Milan in the Champions League on Tuesday night, sparking fears ahead of the World Cup next month.
He appeared to land awkwardly on his right leg and, despite briefly carrying on, succumbed to the injury on the hour mark.
Initial hopes were that the problem was not too serious – but the Daily Mail now reports it is worse than first thought and James could require surgery.
Responding to the news, Potter said: “He’s due to see a specialist over the weekend.
“Until we get that information there’s not much more we can add.
“We’ll wait and see.”
Potter added: “He spoke yesterday and said he didn’t feel too bad.
“But until you get these things checked, you don’t know.
“We’ll wait and see. There’s no point looking into the doomsday scenario yet.”
England are already sweating on the fitness of two other right-backs.
Man City’s Kyle Walker has undergone surgery on a groin problem, while Liverpool’s Trent Alexander-Arnold is out for a minimum of two weeks.
James has been in sensational form for Chelsea this season and, if fit, looks set to be Southgate’s first-choice right-wing-back in Qatar.
The Three Lions’ group opener against Iran takes place in little more than five weeks’ time.
Chelsea, meanwhile, face a run of nine games in the next month.
In another injury issue for Chelsea, Potter revealed France midfielder N’Golo Kante has suffered a relapse in his recovery from a hamstring issue.
“He is due to a see a consultant at the weekend,” added Potter. “It is a setback, it is not good news but at this stage, again I can’t tell you anything more.
“Historically, these are things that have happened which are a concern, we need to get to the bottom of that. It is a setback in the last stage of his rehab so that is worrying.
“All we can do is get the right diagnosis, get the right consultation and then try and help him get back to full fitness.”