The club have signed Cameroon international James Lea Siliki on loan from Rennes.
The midfielder joins the club on a season-long agreement subject to the relevant international clearances being received.
Boro beat off the interest of a number of clubs to capture the signature Lea Siliki.
The player has clocked up almost a century of appearances for Rennes and was a Coupe de France winner in 2018/19.
Boro boss Neil Warnock said: “James is another name that came up and he will be another good addition to the squad. My contacts in France are very impressed with him and we feel he will add to what we have, particularly with his range of passing.”
Lea Siliki is the 12th summer signing and follows Slovenian international Andraz Sporar as the club’s second confirmed deadline day arrival.