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:
The striker spent one year at Boro in the 2015/16 season and helped the Teessiders win promotion to the Premier League. After leaving the Riverside, Nugent has spent the last three years at Derby.
The midfielder joined Boro on loan in 2013 and has played for Championship side Brentford since 2015.
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Baptiste's Boro career was blighted by injuries before he moved to QPR in 2017. The defender also struggled to gain regular game time at Loftus Road and was loaned out to Luton last season.
Since he left Boro in 2013, Martin has played in Switzerland, Norway and Scotland. The 30-year-old was released by SPL side Hearts at the end of last season.
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.
After leaving Boro for Wigan in 2016, the winger, 27, signed for Norwich, where he was sent out on loan to Cardiff and Bolton
Morrison has spent 12 years at West Brom after leaving Boro for the Baggies in 2007. He made 19 Championship appearances last season.
Osbourne made nine appearances for Boro during a loan spell in 2009. The midfielder, 30, regularly played for Walsall in League One last season.
Craine played a part in Sheffield United's promotion to the Premier League, making 15 league appearances for the Blades last term.