The first-team squad - excluding the World Cup stars - are due back on July 5 but both Owen and Hargreaves have already been in at the Red Devils' Carrington training ground to work with the fitness team.
Owen has worked ferociously to recover from the knee injury that cut short his season.
The United staff have been impressed with his dedication and are convinced he is ready to take a full part in pre-season and the club's tour of America and Canada.
Owen will be joined by Hargreaves, who is over his 20-month injury crisis.
The England midfielder managed a brief end-of-season bow against Sunderland after crippling tendinitis threatened his career.