The Germany international has been troubled by numerous injury problems in the past, restricting him to just 16 appearances since joining the Citizens from Borussia Dortmund last year.
Gundogan, most recently ruled out with cruciate ligament damage last December, was brought off the bench in the 6-0 win over Watford at the weekend and is now in line to play a part in the EFL Cup tie with West Bromwich Albion on Wednesday night.
Speaking on the eve of that match, however, the 26-year-old admitted that matching his Dortmund peak may now be tough to achieve at the Etihad Stadium.
"It was a long wait – and tough as well," he told reporters of his latest comeback. "That is why it feels so special to return. I was sad just to watch in front of the TV or in the stands. To be honest, you don't feel as part of the group anymore. You are not travelling with the team anymore. You do everything on your own or with the physio. So of course, that is the worst feeling you can have as a football player.
"So, that is also the reason it was that hard over the months. The worst time was of course the day of the injury or when I knew what exactly happened. When I knew there would be six, seven, eight, nine months out. That was the worst feeling. The day after the surgery was not so good either. But then, at one point, you start to do it again. You start to do your rehabilitation. You recover. You have ups and downs, days you feel better, days you feel very bad.
"I think that is normal. It is not just me. There are doubts if I will be again at the level I had before so, of course that is the case. As I said because of these ups and downs, more of the downs, it is sometimes frustrating. The doubts are at this point even bigger. But I had no other choice. I am a football player. This is what I do. This is what I have done all my life. This is my job. For me, there was no other choice than to try again. If I said I am the same player as I was a year ago, I would be lying.
"I mean, through the injury, you don't feel the same. You don't feel as though you are the most powerful guy in the world – not that I ever did. I had two injuries on my knee and I know what to do to prepare myself for the games and to warm my knee up and be generally fit. I will do everything to be as fit as possible. That could be it for all the injuries! I think I am done now! I am ready to continue playing, to keep fit. To enjoy playing."
Gundogan cost City a reported fee of £20m to sign from Dortmund, becoming Pep Guardiola's first signing at the club.