The Frenchman has only recently returned from a serious knee injury which saw him miss over a year of football, and Celtic boss Neil Lennon confirmed that he had returned to France for surgery.
The 42-year-old told reporters: "It was an innocuous thing. He was running for the ball and we heard this pop.
"We thought he had clipped someone's ankle but obviously straight away, he knew something was wrong and he went over to the side.
"He had a complete rupture of his Achilles tendon, he has had surgery in France. We are waiting on how well the operation went but we are looking at maybe six months."
Mouyokolo had only recently joined the Scottish club after he was released from Wolverhampton Wanderers at the start of the year.