There's no reason to doubt Nelson, and if he says he had pneumonia, his word is to be believed.
That said, pneumonia is not Nelson's problem, and I hope that he doesn't use it as an excuse going forward.
While it's true that pneumonia could have been a factor in his poor physical condition last weekend, that doesn't explain how tired he looked last summer against Junior Dos Santos.
During the Dos Santos fight, Nelson was breathing heavily, dropping his hands and often staggered backwards without having been hit. That's called being tired.
The reason he wasn't as tired in that fight as he was against Mir is because the Mir fight last week was a far more grueling wrestling match.
If the Dos Santos fight was a wrestling match, Nelson would have looked just as exhausted, and if he ever has to fight Brock Lesnar, Nelson is going to look even more exhausted if he survives longer than a round.
While Nelson's explanations are legitimate, this isn't the time for excuses.
If Nelson stays fat, he'll look fine if he's winning and able to control the pace, and he'll look exhausted when he's getting wrestled, beaten up and struggling to get off his back.
Losing weight can only help with his conditioning, and any excuse that stops Nelson from losing weight is a roadblock to his possible future success as a fighter.
Roy Nelson: Mike Dolce is calling.