The Wigan midfielder broke his leg following an accidental challenge with Liverpool star Raheem Sterling during Saturday's 3-0 defeat at Anfield and Martinez is waiting to discover the full extent of the damage.
The Latics boss says the best case scenario is the player will not need surgery but if he does need an operation to pin it back together, then it will effectively end his season.
"If we get lucky, he doesn't need surgery, that could make it a lot easier," Martinez revealed. "If he needs surgery, that could be five months if it brings plates and nails into it.
"Both players were looking at the ball and the two shins collided. It was a nasty sound. We'll keep our fingers crossed but it doesn't look good."
Watson had been in fine form for Latics when filling in for the injured James McArthur in central midfield and everyone will be keeping their fingers crossed for good news.