Bolton manager Owen Coyle fears he could be without influential midfielder Stuart Holden until October.
United States international Holden missed the last two months of the season with a serious knee injury, sustained in a clash with Manchester United's Jonny Evans, which required surgery.
Holden set himself a return date of September but Coyle said the club's medical team were being more cautious.
"He's optimistic and he is improving, no doubt about it, but we have to make sure we pick the right moment to bring him back and not push him at all," Coyle told the Bolton News.
"Stu has targeted the middle of September. My medical lads are a wee bit more wary because they think if he doesn't come back then I'll go off my head, and they're right because I want my players back as soon as possible.
"If we get him back at that point I'd be absolutely thrilled - and the same goes for Sam Ricketts [who ruptured his Achilles tendon in February] as well - but we might just have to be a bit patient.
"Let's not get away from it, we've all seen the effect not having him in the team had on us last season. Sometimes you find that with players, and I've said this about Kevin Davies as well, but when they play all the time you start to take them for granted.
"You just don't realise just how much they bring to your team until they are not there."