Head coach Antonio Conte said on Friday there was "no news" on Costa and responded "I don't know" when asked when the striker might return to London.
A Chelsea spokesman intervened, saying: "Nothing to report on that."
Last week Chelsea dismissed as "nonsense" claims by a lawyer said to be representing Costa that Conte was forcing out last season's top scorer, but reports claim a legal process is ongoing and there is no appetite to discuss the striker.
Conte has said it was decided in January, with Costa and his agent, Jorge Mendes, that the Brazil-born Spain international signed from Atletico Madrid in July 2014 would leave Stamford Bridge this summer.
So far this summer Costa, according to his Instagram posts, has been in Brazil. His rumoured preference of a return to Atletico is complicated by their transfer embargo, which expires in January 2018.