Liverpool defender Kostas Tsimikas broke his collarbone when he collided with Jurgen Klopp on the sideline during the English Premier League game against Arsenal.
Tsimikas was challenged by Arsenal forward Bukayo Saka and stumbled into Klopp, who fell on top of him.
The game on Saturday (local time) ended 1-1 and Klopp said Tsimikas' collarbone was "definitely broken", adding he will be "out for a long time."
Klopp was OK after the 35th-minute incident.
It is unlikely that he will be back for Greece's crucial Euro 2024 playoffs.
Arsenal led after four minutes through Gabriel. Liverpool replied in the 29th when Mo Salah hit his 151st Premier League goal to move up to 10th on the list of the competition's top scorers.