Watson, 27, broke his leg in an accidental clash with Raheem Sterling. The crack was heard by both benches.
Latics boss Martinez revealed: “If we get lucky, he doesn’t need surgery, that could make it a lot easier.
“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.”