However, Sean Dyche has had some positive news on the fitness front, with Steven Defour and Robbie Brady featuring in an in-house game on Thursday afternoon.
Gibson, who arrived from Middlesbrough for £15m in the summer, was hurt in the Europa League clash with Olympiakos in Athens, in which he was sent off.
And Dyche explained: “He’s had a minor operation, It was a minor hernia operation.”
Asked whether he will be out for weeks rather than months, Dyche added: “Weeks, yeah. The specialist says things are pretty simplistic.
“He felt it against Olympiakos. This early in the season, you can’t carry it.”
Defour played an hour in the Under 23s on Monday afternoon, and will continue to build up his game time, with Brady also getting a run out: “Steven’s going well. He won’t be involved yet but he’s getting closer.
“There’s an in-house game for him and Robbie Brady. Steven’s been training a couple of weeks with the first team. He’s in a good place and Robbie’s not far behind.”
Defour and Brady’s return would be a huge boost to the side, and Dyche noted: “I think the squad we’ve got is good in all areas, but you want players who can add to that group of course.
“It’s not just the performance levels, it’s the competitive element. There’s a mixture of reasons why Steven and Robbie add to your group.”