The 20-year-old, a product of Boro's youth system and a Cyprus Under-19 international, has made four appearances off the bench this season and scored his first goal in the 4-1 Capital One Cup defeat by Southampton in August.
Thalassitis had a spell on loan with Boreham Wood last season, scoring five goals in 11 appearances for the Blue Square South side.
He also played two games on loan for Cambridge in September.


 




