Massimo Luongo has signed for Boro on a short-term contract.
The Australian international arrives at Rockliffe Park on a deal until January.
Luongo, 29, came through the ranks at Tottenham Hotspur before gaining Sky Bet Championship experience with Queens Park Rangers.
He most recently played for Sheffield Wednesday, departing the Owls at the end of the 2021/22 season.
A central midfield player, he provides additional experience and competition for Chris Wilder's side in an area the Boro boss had spoken of his desire to strengthen.