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The Spain international finally found some form on Saturday, scoring a brace in Chelsea's 2-2 Premier League draw against Watford.
The 27-year-old has been linked with a return to Atletico, where he starred before his move to England in July 2014.
Atletico president Enrique Cerezo was unwilling to rule out a return for Costa.
"Right now, Diego is a Chelsea player and he has to focus on Chelsea," he told RTVE.
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"But you never know what will happen in football and sometimes players do return to their former clubs."
Costa scored 43 league goals in three seasons for Atletico, who sit second in the La Liga table.