Benvenuto in neroverde! 🖤💚
— U.S. Sassuolo (@SassuoloUS) August 16, 2020
The 25-year-old leaves Fortuna after four seasons following their relegation to Germany’s 2. Bundesliga.
A clause in his contract allowed him to leave Fortuna for a reported €1.5m, although his move was held up as they disputed that.
Ayhan has now signed a long-term deal with Serie A side Sassuolo.
Predominantly a central defender, Ayhan can also play as a holding midfielder and right-back.
Ayhan made 31 appearances for Dusseldorf in the 2019-20 season with a return of two goals and three assists.
Since 2016, he has won 28 caps for Turkey after opting to represent them over Germany.