The 'Daily Mail' claims that the bustling striker has been banned from training with Chelsea's first team as he looks to seal a move away from the club this summer.
This comes just a day after Chelsea confirmed the signing of Real Madrid striker Alvaro Morata on a five-year deal.
Costa finished as Chelsea's top scorer with 20 goals last season but Antonio Conte decided in January that there was no long-term future for the former Atletico Madrid man at Stamford Bridge following a well-publicised falling-out over a potential move to CSL side Tianjin Quanjian in January.
The 28-year-old did not travel to Asia with the rest of the Chelsea squad for their pre-season tour as he continues talks over an exit.
Chelsea are determined that Costa will not undermine another title challenge with his demands and are thus talking to teams over a potential sale.