Richardson played with Keane at Manchester United and under him during his spell as Sunderland manager.
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"That season when I signed for Sunderland, I think I only played 10 games because I had a hairline fracture in the L5 vertebrae in my spine," Richardson told Villa's official website.
"Throughout that season I was very upset, I put on a lot of weight and I got bigger but, just before the end of that season, Roy took me into his office and we had a massive conversation.
"He inspired me to go away in the summer and come back in better shape than I had ever been in.
"I went and played very well in the next season.
"He gave me some good words of encouragement to go and do that over the summer and I appreciate that."