Earlier this week Boro agreed a deal to sign goalkeeper Joe Lumley when his contract at QPR expires in June, a shrewd signing given Neil Warnock needed to strengthen his options between the sticks.
Boro are also looking to sign three new strikers this summer and were interested in frontman James Collins, whose contract at Luton was set to end.
Yet the 30-year-old has instead agreed to join Championship rivals Cardiff City, meaning Boro have been forced to assess other targets.
Warnock said at the end of last season he wants to sign around eight or nine new players ahead of the 2021/22 campaign.
Here are some of the names who have been linked with Boro over the last few weeks and their situations as it stands.
5. Famara Diedhiou - Free agent
A player Boro have been monitoring since January and is now a free agent after he was released by Bristol City. Diedhiou's wages could put Boro off the move, yet the Teessiders are keeping an eye on the situation. Photo: Alex Burstow
6. Charlie Wyke - Sunderland
An easy link to make given Wyke is from Teesside and will be out of contract this summer. Even so, it's understood that Wyke isn't on Boro's radar. Photo: Justin Setterfield
7. Josh Windass - Sheffield Wednesday
After scoring nine Championship goals for a struggling Sheffield Wednesday side, the forward was linked with a handful of clubs including Boro. Reports in Sheffield have since claimed that Windass, who has a year left on his contract, wants to stay at Hillsborough. Photo: Alex Pantling
8. Junior Hoilett - Free agent
Someone who Warnock knows well from their time together at Cardiff. Boro are looking to sign new wide players this summer, yet it's unclear if Hoilett is a serious target. Photo: Charlotte Tattersall