The Barcelona stalwart appeared to pull up on his knee at the Krasnador soccer city, Spain's headquarters for the Russia World Cup, reports Efe.
The 31-year-old tested his apparent discomfort by kicking the ball, after which he decided to leave the pitch.
Manchester City's attacking midfielder David Villa also left the training ground early, although he showed no obvious signs of discomfort.
Spain looks to repeat its success at the 2010 World Cup in South Africa but will have to overcome Portugal, Iran and Morocco first to make it through the group stages.
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