And, after seeing a specialist, he will miss Saturday's game with Wycombe and the final match of the campaign at Barnet on May 2.
Manager Dean Glover told The Sentinel: "We're going to rest Marc. His Achilles problem has improved a lot, but I feel it would be too much of a risk in case it flares up at the end of the season.
"We're looking at pre-season now. The firm ground has kicked in, which has contributed to his Achilles flaring up.
"His rehab work has gone well and he is on the mend. But it isn't worth the risk of it flaring up in the last two games."