What is his stamina? If his stamina is low, then I recommend playing him 50-65 minutes a week. If his stamina is high, then he should be able to play 70-80 minutes and be OK.
A few seasons ago, the BBs announced that players with higher stamina could play longer minutes and their game shape would be fine.
I assume you've been managing his minutes well, so it might just be bad luck + randomness.