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:
1. Duncan Watmore
The former Sunderland forward didn't have much luck with injuries during his time at the Stadium of Light but made an impact when fit. Boro boss Neil Warnock is still keen to add some creativity to his squad before the end of the window. Photo: JPI Media
2. Gabriel Osho
Warnock has admitted Boro have looked at signing another centre-back due to a lack of natural options in that position. Osho, 22, was surprisingly let go by Reading in the summer after breaking into the first team at the end of last season. Photo: Stu Forster
3. Nathaniel Mendez-Laing
A player Warnock knows well from his time at Cardiff. The 28-year-old winger saw his contract terminated in September after making 92 appearances for the Bluebirds. Photo: Alex Livesey
4. Jackson Irvine
The Australian international played as a striker earlier in his career but moved back into midfield while playing for Hull in the Championship. Irvine, 27, can play as a deep-lying midfielder or in a more advanced role. Photo: George Wood