i just took over a team that is a COMPLETE rebuild. so i'm pumping minutes into my freshmen to accelerate their improvements. i've done this successfully in the past, but this is the first time i've ever gotten a message from the assistant coach: "Coach, I'm a little concerned about Robert Zeidman. I don't think he's in good enough shape to be playing 31. You should think about reducing his minutes or spending more time on conditioning. Just my 2 cents!"

i'm not concerned about performance on the court - this is a throw away season - but will this have any adverse affect on his improvement? 

It's just a message about stamina - you're probably consistently playing the guy heavily fatigued running that many minutes at sub-70 stamina.  It won't affect his improvement, though.  It's not clear at that number of minutes how much difference it really makes (IE how much marginal benefit there is from playing 31 instead of, say 22), but you're certainly not holding him back by overplaying him.

The one big caveat here is that, depending on who you ask, he may well be more likely to get injured.  I mean, he's obviously more likely to get injured playing more minutes.  But quite likely it's far from linear, and he's more likely to get hurt in those tired or very tired minutes.  And with poor durability, he could be a legitimate injury risk at this usage.  That being said, injuries are so rare in general that I wouldn't spend a lot of effort thinking about it.  What I do think is a significant concern is the distinct possibility of sharply diminishing returns in terms of improvement/minutes beyond the mid-20s, and whether you could be improving your team as a whole more efficiently by playing him more judiciously.

From customer service:

fatigue does not affect chance of injury

Thanks for the info. Not worried about the team - everyone other than my freshmen are throw aways.