The 31-year-old, who made eight appearances for the team last season, is now out of contract, but has been invited for pre-season training.
"The opportunity was there for him and he has certainly worked hard on getting the weight off," Baker told the club's official website.
"He has been in to the training ground and he is looks far trimmer and fitter. He knew he was carrying too much weight last season and was playing catch up with his fitness but he has made that change.
"So who knows, a fit Nathan Ellington could be the answer we are looking for because we know he has quality."
Ellington has previously played for Wigan Athletic and Watford.