Prime Alexander Karelin v Teddy Riner MMA?

If these two monsters were to fight each other in MMA who would win?

Say they only have a couple months to prepare so they are basically only going in with the skill set they already have.

Karelin might be stronger but Riner is bigger and has a more complete skill set with takedowns and ground game/submission

I have heard Karelin did a little boxing and sambo but I dont think he ever competed at any sort of high level in either.