The veteran goalkeeper, 35, has enjoyed a lengthy career that began with Preston North End in 2000 and included two spells with Leeds United, a year apiece with Fulham, Wolves and Middlesbrough, among others.
Lonergan told the Lancashire Evening Post, "It has been a brilliant experience and it is a job where you've got to reach the highest of standards every day.
"If you aren't on your game in training, you will get found out straight away. You've got a world-class forward line firing shots at you in training every day.
"I've been at clubs before where you've had a couple of players who maybe aren't great in training but will produce in a game.
"At Liverpool , every player is on it in every training session, the standard of work and finishing in training is brilliant. They are a great bunch of lads, very down to earth people who are at the top of their game."