And while the Teessiders are looking for new recruits ahead of the new campaign, many of Boro’s former players are also looking to move on. Scroll down to see which former players are set to become free agents this summer:
5. Albert Adomah
Adomah, 31, also helped the Teessiders win promotion from the Championship in 2016 and was also part of the Aston Villa side which reached the top-flight last term. However, he wasn't offered a new deal. Photo: George Wood
6. Yanic Wildschut
After leaving Boro for Wigan in 2016, the winger, 27, signed for Norwich, where he was sent out on loan to Cardiff and Bolton Photo: AFP Contributor
7. James Morrison
Morrison has spent 12 years at West Brom after leaving Boro for the Baggies in 2007. He made 19 Championship appearances last season. Photo: Charlie Crowhurst
8. Isaiah Osbourne
Osbourne made nine appearances for Boro during a loan spell in 2009. The midfielder, 30, regularly played for Walsall in League One last season. Photo: Nathan Stirk