"When he was signed for big money Villa didn't have anyone to score goals, so he was the focal point in the team," said Withe to the Birmingham Mail.
"All of a sudden in football different managers have different ideas about players and he's maybe not seen as an integral part by Paul Lambert.
"When you go from being the main goalscorer to being on the bench it has an effect on you mentally.
"There is loads of speculation about the transfer fee and all that but at the end of the day it's about you getting into the team and performing.
"If that is not going to happen with Darren Bent at Villa any longer, for whatever reason, then it is probably best for him and the club if he does move on and seek a new challenge."