Emmanuel Ledesma will join Dean Whitehead in departing Boro this summer after his contract expires this month.
The 27-year-old attacking midfielder hasn't been offered a new deal by the club and he is now free to move on to pastures new.
Ledesma made 64 appearances for Boro after joining from Walsall in the summer of 2012.
He made just two appearances for the club last season - his final one coming against Blackpool in September - and he also had loan spells at Rotherham and Brighton.
Head Coach Aitor Karanka had previously confirmed the decision not to extend Whitehead's stay at the club, while club captain Jonathan Woodgate is also out of contract.
Seb Hines, who joined Orlando on a six-month loan deal in February, is also free to find a new a club, while Ryan Brobbel, who spent time at Hartlepool on loan last season, hasn't been offered new teams.
The full list of professionals not to be offered new contracts is below:
- Dean Whitehead
- Emmanuel Ledesma
- Jonathan Woodgate
- David Atkinson
- Ryan Brobbel
- James Warnett
- Kieron Weledji
- Seb Hines