I don't think it was necessarily planted by Gretz. This has been Haley's mentality as a coach... if you don't play well, you don't play, no matter how much you make or how high you were drafted. Every player seems to be on a very short chain. I think he'll give Cassel more leeway than most, but the fact still remains that Brodie has outplayed Cassel so far.
I do hope that Cassel has a good game Sunday because despite the 2 picks, he does seem much more poised in the pocket than Brodie does and isn't afraid to take some shots deep.