Twenty-year-old Aussie Miller is in the middle of his first season in MotoGP, running with LCR-Honda.
However, with the Italian squad is unlikely to find the budget for a two-bike programme in 2016 and having already retained Cal Crutchlow, Miller - who has a contract with Honda - is set to be moved to the Aspar squad by the manufacturer.
The other seat, meanwhile, could go to 25-year-old Frenchman Zarco, who currently heads the Moto2 standings by 85 points.
By Aspar team boss Jorge Martinez's admission, Zarco is at the top of his list - yet the rider has previously told Motorsport.com France that he could stay in Moto2 for another year, even if he emerges as a dominant champion.
Should Aspar be unable to court Zarco, the team has two other options in Moto2 race winner Sam Lowes or runaway Moto3 leader Danny Kent - both Britons.
Kent, however, is widely expected to step up to Moto2 with his current Leopard Racing squad, having reportedly turned down a deal with MotoGP squad Pramac.
Current duoNeither 2006 MotoGP champion Nicky Hayden, nor 2012 World Superbikes runner-up Eugene Laverty are likely to be retained by Aspar.
Hayden, 34, told Motorsport.com he wasn't ready to leave MotoGP, but has not ruled out a switch to World Superbikes.
And that switch now looks a likely option, with the American reportedly continuing to struggle with a wrist injury that stymies his chances at remaining in MotoGP.
The other current rider - Laverty - had reportedly signed a two-year deal with Aspar, but is set to depart after just one season, with Aspar boss Martinez saying the Irishman has not managed to deliver in the races.
Additional reporting by Léna Buffa
