The Blues leave for China on Monday and manager Antonio Conte has reportedly told both players that they will not be selected.
According to Sky Sports News, Costa has not been present at Cobham this week, having been excused from the first week of pre-season training amid mounting speculation over his future.
Matic, meanwhile, has been back in for pre-season training but has reportedly spent much of his time at Cobham this week working away from the main group.
The Spain striker is being tipped for a return to Atletico Madrid, even though they are under a transfer ban, while Manchester United are rumoured to be in discussions for the Serbia international.
Chelsea open their pre-season programme against Arsenal in Beijing on July 22 before travelling to Singapore for games against Bayern Munich and Inter Milan.