Mo Salah was taken off on a stretcher during Liverpool's Premier League fixture with Newcastle.
The Reds talisman clashed with Magpies keeper Martin Dubravka during a battle for the ball in the air.
Salah appeared to be caught in the head by Dubravka's trailing leg as he punched a cross into the box.
The Egyptian immediately lay prostate after a heavy landing before curling up.
He appeared to remain conscious throughout, but there were worries he could be concussion - with a spotlight on head injuries after Jan Vertonghen's incident against Ajax earlier this week.
Salah was replaced by Divock Origi having been treated on the pitch for almost five minutes, with the sub scoring a late winner.
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Salah watched the remainder of the game in the Liverpool dressing room and will be assessed by medical staff.
Liverpool wrote on Twitter: "Origi replaces Salah, who can't continue after a collision with the Newcastle goalkeeper."
Gary Lineker tweeted: "Great sportsmanship towards Salah as he’s stretchered off from Newcastle fans. Let’s hope he’s ok."
Salah is one of Liverpool's most important players as they attempt to win their first league title since 1990.
The winger has netted 25 goals in 49 appearances for the Reds this season.
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Liverpool twice saw their lead cancelled out by Newcastle in a topsy-turvy match at St James' Park before Origi's winner.
Virgil van Dijk opened the scoring in the 13th minute with a free header, but Christian Atsu pegged the Merseyside club back.
Salah then popped Jurgen Klopp's men ahead again only for Salomon Rondon to powerfully strike the hosts level again.
However, Origi climbed off the bench to land the decisive blow.
