England and Bath back Anthony Watson will be out of action until at least Christmas after sustaining a knee injury in their defeat by Harlequins.
Watson underwent an MRI scan on Monday to assess the extent of the injury, however he does not require surgery.
Meanwhile, club captain Charlie Ewels also limped off with a knee injury and has suffered a medial ligament tear.
"Both are collision injuries which happen and there's nothing we can do," director of rugby Stuart Hooper said.
Speaking to BBC Radio Bristol, Hooper continued: "Anthony is in a brace but doesn't require surgery and we get him back ready to perform as soon as possible.
"Charlie has a similar mechanism of injury. It's a knee injury. He's going to see the surgeon tomorrow to see what the best steps are next."
Watson has had problems with an Achilles injury over the past two seasons, which he ruptured for a second time during a photo shoot with NFL players.
"It's a short term thing that Anthony is working on and we need to get right. He is absolutely one of the most diligent professionals around," Hooper added.
"Anything to do with himself or getting ready to play on the field. Alongside our performance department will be working on it 24/7 to get him back as soon as possible."