It’s no secret that Boston Celtics head coach Doc Rivers is on the fence about returning next season — Rivers has three years and $21 million left on his contract. According to ESPN, Doc may be leaning towards quitting: “Although Boston Celtics team president Danny Ainge has stated that Doc Rivers will return to coach Boston next season, Rivers believes it ‘may be time for a change,’ according to a source close to the situation. ‘Doc loves coaching,’ the source said. ‘He loves coaching in Boston. But he feels it may be time for a change.’ Rivers, who has been attending the Celtics’ pre-draft workouts, is unsure of what he wants to do and has not yet ruled out returning to Boston for a 10th season. He has a very close relationship with Ainge, and the source said that is one factor that is making his decision so difficult. [...] If Rivers became available, he would immediately become the most coveted coach on the market. The Brooklyn Nets and Los Angeles Clippers asked for permission to speak with Rivers about their coaching jobs last month, but Ainge refused to grant it. There is a feeling throughout the league, however, that because of the closeness of their relationship, Ainge would allow Rivers to leave and go elsewhere if the coach requested it.”