Manziel's season was ended by a hamstring injury sustained against the Carolina Panthers on Sunday, ahead of the Browns' finale against the Baltimore Ravens.
While the 22-year-old claimed to have cleaned up his party-boy image, Manziel said he has learnt plenty from his seven quarters in the top tier of American football.
"I'm not the Johnny Manziel that came in here a year ago," Manziel said on Tuesday.
"It's been a year of growing up for me. I have to take this job a lot more seriously than I did at first."
Part of growing up means Manziel had to realize he wasn't in college anymore.
He said he "still had a college mindset a little bit and that is absolutely faded from my mind."
As far as his future with the Browns? He hopes the franchise doesn't go after another quarterback.
"I don't think it would be fair to give up on someone after seven quarters of football," he said.
The current Browns situation for quarterback is a bit murky.
Manziel is officially listed as out for week 17 and Brian Hoyer's chances appear to be slipping due to a shoulder problem.
Cleveland looked towards Rex Grossman, but he had other plans.
The Browns will likely see Connor Shaw start as playmaker against the Ravens with Tyler Thigpen, who the Browns signed Tuesday, as the back-up option.