The influential pair, along with Oriol Romeu and Ryan Bertrand, have been selected for their respective countries for the London 2012 football tournament, which runs until just a week before the new campaign kicks-off.
And Blues manager Roberto Di Matteo has stated the situation is "not ideal", especially in the case of Mata, who was also involved in Spain's recent Euro 2012 campaign.
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"How long we give him off depends when they go out of the Olympics and how he feels physically and mentally.
"It is not ideal, but there will be many clubs in the same situation as us."
Mata did not feature in Poland and Ukraine until coming on as a substitute during the closing minutes of the competition's final to score as Spain crushed Italy 4-0.