Hayes (back) will begin a rehab assignment with High-A Dayton on Friday.
Hayes has been sidelined since late May due to a bulging disc in his back, but he's been cleared to resume game action. He will likely require several rehab contests before returning to the Reds, and Hayes faces an uncertain playing time outlook when he is activated with Sal Stewart, Eugenio Suarez and Nathaniel Lowe all healthy.