Timo Hildebrand has completed his move to Schalke on a contract until the end of the season after successfully completing a medical.
The club announced earlier on Friday an agreement had been reached with the former Germany international, with the move dependent on the physical assessment.
Schalke moved for the former Stuttgart, Valencia and Sporting Lisbon goalkeeper in the wake of a serious knee injury suffered by regular No.1 Ralf Fahrmann.
That left coach Huub Stevens with only youngster Lars Unnerstall and the more experienced Mathias Schober available.
Hildebrand penned a deal until the summer 2012, but is ineligible for Sunday's game at Bayer Leverkusen.
General manager Horst Heldt told Schalke's official website: "It would have been too great a risk to have only two goalkeepers, Lars Unnerstall and Mathias Schober, in the squad for an extended period.
"That is why we decided to take this step.
"With Timo Hildebrand, we are getting a goalkeeper whose qualities are known. He has proved himself a very good goalkeeper age and made a key contribution to Stuttgart winning the German championship in 2007."
Hildebrand has been training with second division side Eintracht Frankfurt in recent weeks since being released by Sporting in the summer.
The 32-year-old last appeared in the Bundesliga for Hoffenheim in 2010, but they chose not to extend his contract in May 2010.
"It's just a really nice feeling to be back," Hildebrand said. "The last months were not always easy, so I will enjoy it even more now."
"I was super happy [when Heldt first called me] because I have been waiting a long time ago and turned down some offers.
"For me it was important that my feeling is right. That was 100% the case with Schalke from the first moment. Now I'm just happy to be able to pursue my passion again."