Andoni Iraola said the injury to Joe Gomez was the “worst news” after he began his Liverpool reign with a 4-2 win over Sunderland in Nashville.
Gomez, 29, was forced off within 10 minutes of Liverpool’s first friendly of pre-season after appearing to suffer a muscle issue.
Gomez, who is Liverpool’s longest-serving player, has struggled with injuries throughout his time at Anfield.
Liverpool’s defensive options are thin, with captain Virgil van Dijk yet to return following the World Cup.
New signing Jeremy Jacquet is still building up his fitness while Giovanni Leoni is still recovering from his ACL injury suffered early last season.
“Probably the worst news has been straight away the injury of Joe,” Iraola said after the win.
“We were happy because we were kind of going through all the training without losing any player. Unluckily for us, straight away we’ve lost Joe.”
Iraola confirmed that new centre-back Jacquet is unlikely to feature until Liverpool’s final game of their pre-season tour as he recovers from a shoulder injury.
Goals from Dominik Szoboszlai, Federico Chiesa, Kieran Morrison and Lewis Koumas secured a 4-2 win for Liverpool, who will be back in action against Wrexham on Thursday.
Alexander Isak, Florian Wirtz and Ryan Gravenberch will begin training with Liverpool on Sunday after joining the pre-season squad.
