There's no word from the Chiefs on the injury other than that it's to his ankle. He left the Chiefs Week 7 game against the Jacksonville Jaguars with some sort of leg/ankle injury.
It'd be a disappointing time to lose McCluster even if for one game. To this point, he hasn't been much in the fantasy football world but there have been indications that the Chiefs want to get him more involved in the offense.
They showed that in Week 7 by giving him a season-high nine touches against the Jaguars. I imagine he was likely to continue on that path of an increased role.
There's no telling what an injury might do to his role in the offense.