The Teessiders are primarily looking at signing players on loan from Premier League clubs, but could also look to the free agent market.
Here are nine players who are still without a club and who have Championship experience – scroll down and flick through our gallery to see the full list:
5. Kieron Freeman
After helping Sheffield United reach the Premier League, the 28-year-old defender rarely featured for the Blades in the top flight last season. Freeman has played as a right-back for most of his career, a position where Boro do appear a little short of options. Photo: George Wood
6. Kevin Stewart
The former Liverpool midfielder was linked with Boro a few months ago after his contract expired at Hull. The Teessiders appear well stocked in central midfield but Stewart has also played at centre-back and is versatile. Photo: David Rogers
7. Chris Solly
Another right-back without a club after leaving Charlton before the end of last season. The 29-year-old captained the Addicks at times last season. Photo: Luke Walker
8. Andre Green
A young striker, 22, who has Championship experience after loan spells with Preston and Charlton last season. Green was released by Aston Villa in the summer. Photo: Gareth Copley