I know he has come out and publicly stated that he's regained all his weight and is over the whole summer Mono thing.. but I don't believe that to be true.
I noticed that Brook Lopez plays best in the 1st quarter. Usually scores most of his points in the 1st half. In the 2nd half he disappears, and by the 4th quarter... he's done. This is clearly a conditioning issue.
Looking further into it, here are the stats from nba.com
On back to backs he averages: 15.5 ppg
1 days rest: 18.8 ppg
2 days rest: 23.0 ppg
3 days rest: 25.0 ppg
Clearly the more rest he has, the better he preforms.
Mono is no joke... don't give up on Brook. Let him get his wind back. He will still be the dominant center we all thought he would be.