Central Coast player Matt Millar was sent home from training on Thursday after the club discovered the fullback had no interest in renewing his contract with the Mariners, having already signed with their F3 derby rivals Newcastle.

Just two days out from their home clash with Melbourne Victory, Mariners coach Mike Mulvey did not let Millar train with the rest of the squad after learning he had signed with the Jets for next season.

Newcastle bound: Matt Millar will leave the Mariners for rivals Jets next season. Credit:AAP

It is understood the club was furious to learn of Millar's move north next season, having signed the fullback from the NPL and giving him a chance in the A-League. They were prepared to offer the defender a bumper contract extension which would have more than doubled his current earnings.

Millar's performances have arguably been the silver lining to an otherwise disastrous season for the Mariners. However, those displays quickly piqued the attention of the Jets who wasted no time in making a move for the 22-year-old, immediately approaching him from December 1 when players became free to talk to rival clubs.