Teamtalk are reporting that Boro are looking to strengthen their defensive options following the departure of Ben Gibson, with Tomas Kalas being high up on the list.
The Chelsea player was on loan at Boro for the 2014–15 season when Aitor Karanka was in charge. He was on loan at Fulham last season but a move back to the Premier League newcomers looks unlikely.
Another former loanee, Mo Besic, has also been linked with a move back to Boro.
Everton value Besic at around £12 million, with the Bosnian already having a spell playing under Tony Pulis last season.
Upon joining Boro on loan last season, Besic said "from what I’ve seen, it’s a big club and it’s a good opportunity for me. I could have gone elsewhere, but I decided to stay in England and because of Tony Pulis I came here."
"I think he’s a fantastic coach."