Naby Keita had to be taken off on a stretcher in the early stages of Liverpool's Champions League match at Napoli.
The midfielder went down off the ball just 19 minutes and immediately appeared to be in distress, seeming to indicate a problem with his back.
After receiving treatment on the pitch, Keita was eased on to a stretcher and then driven off on the back of a buggy, with Jordan Henderson taking the 23-year-old's place.
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It is a disappointing blow for Keita, who is yet to make much of an impact following his big move from RB Leipzig.