The Swatragh player was injured during a second half clash with Galway midfielder Paul Conroy which resulted in the St. James' man being sent off on a straight red card by Tyrone referee, Sean Hurson, with McWilliam's eventually being forced off by the injury in the 67th minute
It means McWilliams, who had been enjoying an excellent League campaign with Rory Gallagher's team, will miss next Sunday's final day trip to Meath, a match Derry have to win whilst hoping Galway can do them a favour against Roscommon, though he should be fit for the start of the Ulster Championship on May 1st against either Tyrone or Fermanagh.
Conroy's dismissal was one of three at Owenbeg on Sunday, Derry's Gareth McKinless also seeing a straight red for his part in a melee involving both sets of players while Ciaran McFaul received an injury time black card for dissent having already been booked.
In his post match interview, Galway boss Joyce had indicated the Tribe would be appealing the red card for Conroy which would rule him out of the Roscommon match.
"We'll go and try to win the game (against Roscommon) and the following week with the final but some lads have played now five weeks in a row," he explained, "Next week would be six weeks in a row so we have to look at a couple of injuries, look at the red card and appeal that definitely because I thought it was very harsh on Paul.
"His hand did make contact with the Derry player but I don't think it was a striking action, it was more to try and get some separation from himself and they Derry player and Paul actually won the free."