Manchester United boss Ole Gunnar Solskjaer became fed-up with the attitude of Romelu Lukaku towards the end of their time together.
Lukaku was sold by United to Inter Milan last summer.
The Times says a rift between Solskjaer and Lukaku in United training was what led to the striker's departure from the club last summer.
United sold Lukaku to Inter Milan for around £75million in August, with the Belgian and his former club profiting from the parting of ways.
Lukaku attempted to avoid being picked by Solskjaer towards the end of last season due to a few minor muscle injuries - which the Norwegian is said to have been unhappy about.