And both are expected to be out until at least the end of February as they continue their rehabilitation.
The Ospreys went down 22-9 to Leinster on Friday night and have some ground to make up in the GUINNESS PRO12 but medical performance manager Chris Towers explained that both players are still a little way off a return.
"(Webb's) recovery is going well and we're now concentrating on getting him to the physical level he needs to be in order to perform as we want," said Towers.
"He has begun running again, starting doing some skills work, and the focus is on getting him available for selection at the end of February, which would be five months post-op.
"Tyler is suffering from an effused knee post surgery and on the advice of the specialist responsible for his care we need to give him time to let the swelling settle down, which means that he is looking at another six to eight weeks before he will be in a position to return to playing."
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