Isaac Williams, who boxed at Leicester Railwaymen's Boxing Club, was stabbed in Evington on 21 April and died on Monday.
Former coach Jon Whike said: "He was easy to coach, always smiling, with a big grin on his face."
Devan Garner, 19, of Octon Close, Hamilton, Leicester, has been charged with his murder.
Charlotte Ford, 22, also of Octon Close, has been charged with perverting the course of justice and a second man arrested on suspicion of murder remains in police custody.
A tribute on the Railwaymen's Boxing Club's Facebook page said: "Rest in peace Isaac a polite talented young man - our thoughts are with family and friends."
Mr Whike said: "His last fight with us in 2013 and then he left to concentrate on college and work - I guess he had other commitments."
A 20-year-old boxer who was stabbed to death in Leicester was a "quiet, polite lad", his former boxing coach said.