The 23-year-old completed his first 90 minutes for the Black Cats in their goalless draw at Burnley on Saturday.
Rodwell, who made just seven Premier League starts during two years at City, believes that his match fitness is returning after lasting the duration at Turf Moor.
"I felt good out there. I'm getting fitter and have played my first 90 of the season," he told the Shields Gazette. "I had a couple of chances, one when I could have took it earlier. On another day, I might have got a goal.
"It's been hard. Fitness-wise, I've been on the training field every day, but it's match fitness. You can't buy that. You can train as much as you want, but it's not the same. The anticipation and just being alert comes with games.
"It's felt like a long lay-off. It's hard when you play one game and then miss the next six. But I've had four or five games now and long may it continue really."
Sunderland host Stoke City in the Capital One Cup on Tuesday evening.