Ospreys physio Chris Towers is consulting with specialists after the player underwent a scan, which is expected to confirm that Webb has damaged his anterior cruciate ligament. If this is the case, he will require reconstructive surgery that will keep him out until late December.
Speaking about the injury, Webb said: "I'm absolutely gutted, I really am, especially as I have already had the same injury in my other knee a few seasons ago, but there's absolutely nothing you can do to prevent it happening. My studs caught in the turf when I took a tackle and that was that.
"I've been told by the physio what to expect, we haven't had the results of the scan yet but they seem pretty sure that it's an ACL. If that's right then I'll just have to knuckle down, get the op done and then look to get back into action as soon as I can, which hopefully will be around Christmas time."