The Brazil legend rescinded his contract with Mexican side Queretaro and had been linked to a move to Turkey.
The newly-promoted club are set to complete the signing of Samuel Eto'o as well as the former Barcelona attacker, and president Gultekin Gencer says there will be another big transfer coming soon.
"We reached an agreement with Ronaldinho," he told TRT Spor. "I think within two days it'll be made official.
"Besides Eto'o and Ronaldinho, we will make another big-name signing.
"When it's done, we'll set the world on fire!"
The attacker then appeared in an Instagram video, telling fans: "Hi to everyone. I will be in Turkey with you soon."