"Bid now on my signed (ripped) match worn shirt that I wore in the first leg of our Champions League quarterfinals against Borussia Dortmund! Proceeds go to 8-year-old Dilara, who is fighting against a very rare disease - let's make her live-saving surgery possible!" Gundogan said on Twitter.
Dilara Abanoglu was diagnosed with Ollier disease after a tumor was discovered in her left knee joint when she was one year old. If she does not receive the necessary treatment, her leg may be amputated.
Gundogan's campaign will enable her family to obtain funding for surgery in Turkey.
"There are very few doctors in the world who can operate on Dilara," Gundogan said on the club's website.
A former Borussia Dortmund regular, Gundogan has been playing for Manchester City since 2016.
In his five-year-spell at Man City, the 30-year-old helped his team win two English Premier League titles in 2018 and 2019. He was the German Bundesliga champion with Dortmund in 2012. Gundogan is also playing for his native Germany.