"The gaffer (Paul Jewell) has been different class and I'm not just saying that. He is an honest man, which is great to have in football, and I have a lot of respect for him," Holmes told the Derby Telegraph.
"He spoke to me and felt it was probably best I had a new challenge, and I feel that needs to happen as well.
"It has been very tough for me in recent years, because there have been many different managers.
"For a young player trying to make his way in the game and nail down a position in the team, that can be difficult and it left me always trying to prove myself."