The shot-stopper picked up the knock while preparing during La Roja's 1-1 draw with France and could now be a doubt for the Reds when they return to action at the weekend
The Reds' first-choice keeper was unable to take his usual place on La Roja's bench for the game's second half and will now undergo a physical examination upon returning to Merseyside.
Manchester City's David Silva was substituted in the game after picking up a hamstring injury, while Alvaro Arbeloa was also withdrawn with a similar knock.
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Reina told reporters: "The injury is not serious. I got injured at half-time. Today [Wednesday] I will do more tests at Liverpool."
The Spaniard has only missed four Premier League games for the Reds since May 2007, with a run out of the team being enforced on him towards the end of last season due to suspension.