The Serbian international joined Boro on a three-month loan deal back in October, and Head Coach Aitor Karanka has thanked the player for his efforts during his time with the club.
Milos made four appearances for Boro during his stay on Teesside, three of those coming from the bench.
His debut came at Millwall as a substitute in the 5-1 away win in November and his only start was at Blackburn Rovers in December.
The Boro Head Coach said: "I'd like to thank Milos for his efforts while he was here and wish him all the best for the future. I'd also like to thank Tottenham for allowing him to come here for three months."
The club also has Veljkovic's White Hart Lane team-mate Ryan Fredericks on loan, but the youngster is currently sidelined with injury.