Toure failed a drugs test in March after taking one of his wife's diet pills that contained a prohibited substance and he missed the end of last season including City's win over Stoke City in the FA Cup final when they won their first trophy for 35 years.
The 30-year-old former Arsenal player told City TV: "I feel totally recharged and as fit as I've ever been in my life. Hopefully it will be like having a new signing because I am back and want to challenge for a first-team place.
"I know it won't be easy because the team is playing so well but I'll be pushing hard for an opportunity.
"I'm just so happy to be back and I will give everything I have to the team, this club and our fans. I can't wait to get going," Toure added.
Ivorian officials sought clearance from world football's governing body FIFA before including him in the squad for Saturday's African Nations Cup qualifier in Kigali.
Toure, who last played for his club on February 27 in a 1-1 Premier League draw with Fulham, could return for second-placed City's home match against Wigan Athletic on September 10.
PLAYER'S SHOCK
He said he was stunned when he failed the dope test as he thought the pill had been approved.
"I remember it clearly," added Toure. "I was at home in my bedroom when the club doctor and [manager] Roberto Mancini came in to explain what had happened.
"It was a shock to see them there and I immediately realised the implications for my career, the club and my family.
"It was an awful moment because I didn't know what was going to happen."
Toure thanked the club, City's fans and his brother and team-mate Yaya for their support during his expulsion.
"Yaya has been incredible and as brothers this has brought us even closer. He was always there for me and kept me informed of what was happening at the club.
"I must also thank the manager, my team-mates, the staff and particularly [chief executive] Garry Cook and our chairman Khaldoon Al-Mubarak for standing by me and helping me through this period.
"It's at times like this you know who your friends are and I'd also like to thank people like [Arsenal manager] Arsene Wenger too," added Toure.
