However, following further medical examinations, it has now been revealed that the injury will not require surgical intervention and Mullan faces ten to 12 weeks on the sidelines before his comeback.
"Obviously amongst the disappointment of the initial injury for Matt, there seems to be some better news on the injury," said Ruddock.
"The fact that he doesn't require surgery is a major one and a very positive prognosis.
"With Matt's professionalism, dedication and desire, I know he will push every boundary to get back into action before the ten to 12 week deadline."
Meanwhile, Shaun Ruwers has today (Tuesday) undergone surgery on his tendon injury in his foot but back row Kai Horstmann has not now had to go under the knife, after further tests, and is scheduled for a return in the coming weeks.