We take a closer look at nine players who could have joined Neil Warnock’s side if negotiations had gone differently – scroll down and flick through the pages to see them:
5. Luke Amos (QPR)
Another former target who has been missing through injury. Amos made his loan move to QPR permanent in the summer and started Rangers' first five league games in midfield. Yet the 23-year-old is now set to miss the rest of the season after rupturing his anterior cruciate ligament (ACL) against Bournemouth in October. Photo: Shaun Botterill
6. Yannick Bolasie (Everton)
It's been well documented that Boro tried to sign the winger on deadline day but a deal wasn't completed in time. Bolasie hasn't played for Everton since May 2018. Photo: Nathan Stirk
7. Boli Bolingoli (Celtic)
Warnock admitted he tried to sign the defender before Bolingoli broke strict quarantine rules which led to two Celtic games being suspended. The 25-year-old instead signed for Turkish club Istanbul Basaksehir on loan until the end of the season and has been a regular starter in recent weeks. Photo: Mark Runnacles
8. Jordan Jones (Rangers)
The former Boro midfielder appeared to be surplus to requirements at Rangers and a return to England was mooted. Jones stayed at Ibrox and made consecutive starts in the league before he was suspended by Rangers for "breaching Covid regulations." Photo: Mark Runnacles