Tough call. Keep in mind wins are pretty flukey. Granted McDonald has given up 4 or more runs in his last 4 starts. However, he has the power, when he can keep the walks down he can put up the 10K 1 run gem he put up against SF right out of the all star break.
I would say this though, all those ww pithcers should be owned in leagues with 12 or more. (but so should McDonald).
Try to trade him before you dump him.