The 25-year-old midfielder came on as a late substitute in Barca's 3-0 victory against Athletic Bilbao on Friday, replacing Xavi with only 10 minutes left on the clock in the Copa del Rey final.
Subsequent tests revealed that Fabregas has sustained a femoral biceps problem, with an estimated recovery time of seven to 10 days.
This means that the former Arsenal midfielder will miss Spain's upcoming friendlies against South Korea and China, having been selected for Vicente del Bosque's final Euro 2012 squad, which was announced on Sunday.
Thiago Alcantara, who was also introduced in the final stages of the match, has a slight edema on his right leg, but his recovery time has not been estimated by the Catalan club and he was not included in the tournament party.
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