The club has signed Northern Ireland Under-21 international midfielder Caolan Boyd-Munce from Birmingham City.
The 21-year-old has signed a two-and-a-half-year contract with the club.
Belfast-born Caolan started his career with Glentoran before joining Birmingham City’s Academy. He progressed through the ranks with the Blues before making his debut in August 2019.
Caolan made nine appearances for Birmingham and signed a two-year contract with the club last summer.
The youngster has also represented his country from the age of 15 to the U21s.
Boro boss Chris Wilder said: “We’re really pleased to bring Caolan in. He’s a young left-footed central midfielder who we have been tracking for quite a while now.
“He’s been playing regularly in Birmingham’s Under-23s, we’ve been watching him closely, and we’re delighted the opportunity has arisen for us to sign him.”