Roberts became Manchester United's first England international in 1905.  It wasn't until 1983, when a United captain under Bryan Robson won the FA Cup for the fifth time, that another Englishman brought the club to FA Cup glory as the captains of United's second and third triumphs were both Irish and fourth FA Cup winning team was led by a Scotsman. 

On December 2, 1907, Roberts and Meredith were instrumental in founding the players' association. Although the organization was not recognized by the FA, it received considerable support from other league clubs. In August 1909, the association threatened the suspension of any player who professed membership of the Union, after which Roberts and his Manchester United teammates were invited to a meeting with the club's management. The players refused to give up their membership of the union, forcing the club to turn to the first opponent of the new season, Bradford City, to cancel the game because they couldn't field a team. The FA's threat had reduced membership of the Union so that the only members were the Manchester United players who called themselves "The Outcasts". It was only after Everton's Tim Coleman renewed his support by taking the side of the outcasts that the FA gave in and the Roberts' Union was saved.