Matthew Buck, who works for the PFA, has represented Milner since he was a teenager.
“It was a difficult decision for James," Buck told the 5Times podcast.
“He assessed all his options, looked at his age and how often he was playing, and just felt he wasn't getting as many starts at Man City as he would have liked.
“We had lots of meetings with Man City but towards the end of the season in 2015 James realised that to play regular football he maybe needed to move on for a fresh challenge.
“From January onwards we had interest from Italy and Spain. In total about 14 clubs made contact. At the end of May we had a few meetings with Liverpool and James quickly realised that it was a challenge he wanted to take.
“We met with Brendan Rodgers and Ian Ayre. The club wanted to get back in the Champions League and challenge for trophies. For James, it's been a great move and hopefully he can put that right this season and bring some silverware to the club."