Kieron Dyer feels he betrayed Bobby Robson and was partly responsible for him getting the sack at Newcastle.
The England midfielder infamously refused to play on the right wing when brought on as a substitute in the opening match of the season at Middlesbrough.
He subsequently apologised to Robson, who was sacked at the end of August, but it took a long time for Newcastle fans to forgive him, although his form under Graeme Souness has helped heal the wounds.
"When I think about it now I feel like I betrayed Bobby," Dyer, 26, told the Independent. "That's the worst thing about it. He treated me like a son and I let him down. I have to take some responsibility for him getting the sack."
Dyer revealed: "He knew I was frustrated from the previous season, but I should have just played that game. He had stuck by me through everything and he even tried to defend me after the Boro game.
"He told the press I had a tight hamstring, he tried to shield me and when I think about that, how I let him down, it's the biggest disappointment of my career. I'll have to live with that feeling for the rest of my life.
"It hurts me. When he got the sack, he told me I was one of the only players to ring him and wish him the best. I said thank you for all he'd done, but that's little consolation. I regret letting him down so much."
