Sunderland boss Steve Bruce and striker Kenwyne Jones both hinted at a breakdown in their relationship following the striker's £8million move to Stoke City.
The 25-year-old Trinidad and Tobago international ended a three-year stay at the Stadium of Light after Bruce accepted the Potters' club-record offer.
As well as revealing his frustration with Jones' inconsistency, Bruce said: "Towards the end with Kenwyne, things were not working out so I have accepted Stoke's offer."
He continued: "There has always been a frustration with me, and I think with supporters who have watched Kenwyne, that you see an abundance of talent but it has not come out often enough for us, for whatever reason."
Jones, who has signed a four-year deal at the Britannia Stadium, said: "Sometimes circumstances happen that you have to leave.
"It's never good to leave a place when you've been there for a while but I'm looking forward to doing well for Stoke."
The former Southampton forward became a favourite at the Stadium of Light under Roy Keane following a £6m move in 2007 and was named the club's player of the season the following summer.