Last summer, Nolan had one year remaining on his contract but the veteran midfielder opted to depart as he did not feel a reduced role would be beneficial to him or the club.
"There was no moment of 'oh yeah, that's the final nail in the coffin for me at West Ham.
"Slaven Bilic was first class and I loved working with him," Nolan told The Times. "He said 'I can't guarantee you'll play but you'll always be around my squad.'
"I could have picked up my money, but I didn't feel like I was giving what I can to a team.
"I played 29 times in the Premier League last season, but I can't give what I give from the substitutes' bench.
"There's a drive inside. I needed a challenge, the next step."