The 21-year-old was in China representing a Brazil youth side led by Under-21 coach Alexandre Gallo, who is running the rule over players ahead of the Rio Olympics in 2016.
However, he had to return home to Barcelona because of the injury, meaning he will miss matches against Australia, South Korea and China.
After undergoing tests with club doctors, it was confirmed that Rafinha "has a slight elongation of the sartorius muscle of the right leg".
Barca did not disclose if the midfielder is likely to spend any time on the sidelines as a result.
Rafinha has made seven appearances in all competitions for Barca this season.
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