The Teessiders have already brought in Patrick Roberts and Lukas Nmecha from Manchester City, with loan signings the most viable option. We take a look at nine Premier League centre-backs who haven’t been playing for their current clubs could be available – scroll down and flick through the pages to see them:
1. Ben Gibson - Burnley
Has made just one Premier League appearance since moving from Boro to Burnley a year and a half ago. Looks like he needs a move to kick start his career.
Photo: Alex Livesey
2. James Chester - Aston Villa
A player who has recently been linked with a move to the Riverside. The 30-year-old was a key player for Villa in the Championship but is yet to make Premier League appearance this season.
Photo: Catherine Ivill
3. Jairo Riedewald - Crystal Palace
Palace have had their injury issues this season which may make them reluctant to let players go. Even so, 23-year-old Riedewald has made just six league appearances this season.
Photo: Jordan Mansfield
4. Jack Simpson - Bournemouth
The former England Under-21 international was a regular for Bournemouth at the end of last season but has made just three Premier League appearances this term. Now 23, Simpson will surely be keen to gain more game time.
Photo: Nathan Stirk