Peterborough boss Darren Ferguson is concerned by the hamstring injury sustained by Nathaniel Mendez-Laing on Saturday.
The new arrival from Wolves pulled up in pain in the early stages of the 1-1 draw with Stevenage at the Lamex Stadium.
Posh will send the winger for a scan but Ferguson is already resigned to being without the 20-year-old for the opening games of the forthcoming campaign.
"Nat's injury is a big worry," Ferguson told reporters after the game.
"We'll get him a scan on Monday to find out the extent of the injury but everyone here could see he pulled his hamstring.
"It's very unlikely he'll make the start of the season. You're looking at a couple of weeks out as the best case scenario and if he has torn it badly it will be a lot longer.
"I never like to see muscle injuries and it is something he has had problems with in the past but his medical and scan before we signed him were all clear."
The news comes as a further blow to Peterborough, who have already lost left-back Tommy Rowe with a fractured collarbone earlier this summer.