The scrum-half is now a doubt for the upcoming Six Nations after the WRU confirmed it would "restrict" his involvement in the tournament.
Webb will now undergo further assessments as Wales look for the best solution and he has already been replaced by the uncapped Tomos Williams.
Webb's Wales career could now be over as he is set to join Toulon at the end of the season after agreeing to leave Ospreys.
He will be ineligible for selection as new rules state overseas players must have won 60 caps for their country, with Webb currently on 31.
Coach Warren Gatland has a number of injury worries ahead of the Six Nations with Sam Warburton, Jonathan Davies, Dan Lydiate and Jake Ball already set to miss the fixtures due to injury.