If he is not fit or cant be bothered then as a professional athlete he has broken the terms of his contract.
A thorough Medical would prove whether he is fitness is up to scratch also the players wear vests to monitor fitness during every game and records are kept.'Can't be bothered' is very subjective and getting/ maintaining a player's fitness is as much a responsibility for the club as the player.
If Nesbitt is turning up for training and on match days and staying out of trouble, then I reckon that it would be very difficult to prove that he is in breach of contract.
A thorough Medical would prove whether he is fitness is up to scratch also the players wear vests to monitor fitness during every game and records are kept.
If a players fitness drops off over a short period of time (close season) or no competitive games it would become apparent very quickly that a player has either health problems or is taking the piss, as for turning up late for training, records would be enough proof.
He was apparently very good in training at Aberdeen. Not sure if that's still the case. I don't know any Aberdeen fans to ask. They were pretty lenient on their man Duk which surprised me as I had them down as a well drilled outfit. I don't think Nisbets ever had to make much effort. He was at Ayr Utd a while back and pretty poor there. Kicked on in some shit teams til Millwall and got found out. He's always been spoiled. As much as it pains me to say, Hibs we're poor so he stood out and had free reign. Personally I think he's making himself worthless out in the real world. Can see a transfer termination coming up.Assuming that Nisbett is 1) not on the piss/ drugs and 2) at least looks like he is trying during training, all technology will do is show that the training regime is not working for him. He might not be eating correctly away from the training ground but short of spying on him that would be difficult to prove.
Given those assumptions, as I said previously, imo it would be very difficult for Aberdeen to sack him on fitness grounds as he could argue that his relative lack of fitness was as much the club's fault as his.