The Brazil international has previously admitted he was 'honoured' to be linked with a move to Old Trafford, but will join Schalke when his contract expires next month.
Schalke wrote on their official Twitter account: "Done Deal! The first signing for 2016/17 is complete. Naldo will join Schalke on a free, signing until 2018!"
The Sweden striker will leave the Ligue 1 champions in the summer when his contract runs out and has already confirmed interest from the Premier League.
The 34-year-old, who has also received offers from the Chinese Super League and MLS, is said to have requested guarantees on who will be United's next manager before he puts pen to paper.
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