The Blues will leave for China on Monday.
Costa, 28, wants to rejoin Atletico Madrid, even though they are under a transfer ban; while Manchester United have been on the trail of Matic.
Monaco midfielder Tiemoue Bakayoko is expected to replace Matic in the Chelsea side next season.
It is believed the 22-year-old will complete his move to the Premier League champions in the next few days.
Chelsea open their pre-season programme against Arsenal in Beijing on 22 July before travelling to Singapore for games against Bayern Munich and Inter Milan.