I hope McDonald makes a great recovery, but I prefer this match-up. Brian Foster has flown under the radar with his record of 2-2 in the UFC but his striking needs to be respected. If he lands on you, it will hurt.
This fight could go two ways in my opinion.
1.) Brown will do like he sometimes does and test his striking game if he thinks his opponent is overrated, this could end with him on the wrong side of a combination and the ref stepping in.
2.) Brown can play it smart and take Foster to the ground right from the bell and show his brilliant BJJ game.
This is Browns' fight to lose. I think he can win with ease, if he just sticks to what he's best at, and that's BJJ.
Don't get me wrong, I really like Brian Foster. I think more people should keep an eye on him. But at the same time he's still pretty young and has time to learn the jui-jitsu game that he desperately needs.
All in all, should be a great (possibly very short) fight!