Asked if he would rather Costa, who has been struggling with a hamstring injury, did not play for Spain in the upcoming internationals, Mourinho told reporters: "Everyone knows Diego has been in trouble for quite a long time, but I'm nobody to make that decision.
"Everybody knows what is going on with Diego but I am nobody. The moment a national team wants to select a Chelsea player, I am nobody.
"It is their decision -- they can do what they want. They can call up the player, it is completely out of my control, and what I think and feel doesn't play a part.
"We can send reports, but at the end of the day it is their call. It is their decision, so when they make the pre-selection everything is in their hands. I can do nothing."
Mourinho has said for weeks that Costa, who injured the hamstring playing for Spain against France in a friendly on Sept.4, is struggling to play more than one match a week.
Spain's next two internationals are their Euro 2016 qualifiers against Slovakia on Oct.9 and Luxembourg three days later.
But Mourinho confirmed that Costa, who has scored seven goals in his opening five Premier League games for Chelsea, will start against Aston Villa at Stamford Bridge on Saturday.
"He will start the game without any problems but the question is always the same: Can he finish the game and be in a condition to play against Sporting Lisbon (in the Champions League) 48 hours later?
"He is working with the technical department, with the physios, he is working hard, because mentally he is ready for every game but physically he is not."
Chelsea are effectively involved in a top of the table clash for the second successive home league match with an unlikely opponent after playing Swansea at Stamford Bridge on Sept.13.
Villa are third, with the same number of points as second-placed Southampton, and will be keen to bounce back from last week's 3-0 home defeat to Arsenal.
(Reporting by Mike Collett, editing by Pritha Sarkar)
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