Yep that's the major issue at this stage.He has a decent body shape for it but after 5mins he will be totally gassed. That can change over time with more direct focussed fitness and gym activities also. Not against it but his defensive efforts in simple structured situations and laziness to cover are huge red flags for me. I have alot of doubts that he would regularly get walked past after 25-30mins.
He'd have to have a spell in reserves at the position to get up to speed and realistically an offseason too. Probably wouldn't be an 80 minute player but maybe coming off the bench would suit too as our 14.