I'd stick him on the bench and only really play him when Vlaar is injured. There's no need to rush him back and each match Clark has should/could improve him as a player. Furthermore a leftie and a righty at the back has slightly better balance.
Alternatively I might be tempted to go three at the back. Okore's pace would make him ideal on the right, Vlaar in the middle and I suppose clark on the left I'd prefer someone faster). With so few teams playing natural wingers and our fullback's seemingly better going forwards than back it could play to our strengths and make us different/more awkward to play against.
