The club has agreed a deal to sign Bundesliga striker Delano Burgzorg from Mainz 05, subject to international clearance.
The 25-year-old will join for an undisclosed fee and has agreed a four-year contract.
A former Dutch youth international, Burgzorg spent last season on loan in the Championship with Huddersfield Town, where he scored seven goals in 33 appearances.
The striker, who also qualifies to play for Suriname, shot to prominence as a teenager in the Netherlands before a spell with Italian side Spezia, during the season they won promotion to Serie A.
He impressed further on his return to the Netherlands before securing a move to Bundesliga side Mainz 05.
Boro head coach Michael Carrick said: “We’re really happy to bring him in. He experienced the league last season, and we’re excited about what he’s capable of doing.
“He’s a threat and will be real asset because he has different types of attributes to what we already have. He’s a good addition to the squad and being able to get things done early means he will be here for the start of pre-season.”
Burgzorg becomes the club’s second signing of the summer, following Luke Ayling, who has joined permanently after impressing on loan last term.