Chelsea manager Jose Mourinho has claimed that Romelu Lukaku was unwilling to fight for his place in the squad.
The Belgium international striker signed a five-year deal with Everton for a club record of £28m on Wednesday, following his successful loan stay last term.
Asked about the club's thinking behind allowing Lukaku to leave, the Portuguese coach said that the forward didn't want to prove himself at Stamford Bridge.
He told reporters: "The thinking behind that was, first of all, the fact that Romelu was always very clear with us in his mentality, and his approach was not highly motivated to come to a competitive situation at Chelsea.
"He wanted to play for Chelsea, but he wanted to be first-choice striker, which with a club of our dimension is very difficult to grant a player first-choice status.
"That reduced immediately his desire to come to us. After that Everton come with an important offer and as I always say, as it's the reality of our club, we want to be inside of the rules of Financial Fair Play, and when we have the chance to make some movements that create a positive impact in FFP, Chelsea always analyse these situations."
Meanwhile, Toffees manager Roberto Martinez has claimed that his new forward is "worth every penny".