Melvyn Hargreaves, 71, who lived in the city died from head injuries two days after he was assaulted on Mercian Way in January last year.
Samuel Watts admitted the manslaughter of Mr Hargreaves when he appeared at Nottingham Crown Court on Wednesday.
Watts, of Forman Street, Derby, was remanded in custody and will be sentenced on 6 May.
A 23-year-old man has pleaded guilty to manslaughter after the death of a 71-year-old man who was attacked in Derby.