Mohamed Salah picked up a muscle injury, Virgil van Dijk has been playing with two broken ribs for weeks, Sadio Mane broke his thumb and now Naby Keita has injured his hamstring while James Milner has been out since the Manchester City draw at Anfield.
The 30-year-old was handed his 22nd worldwide cap on Tuesday as Belgium drew 1-1 in a friendly with the Netherlands, with Koeman deciding to rest Real Madrid stopper Thibaut Courtois.
"The surgery, conducted at a north-west hospital and supervised by club medics, was successful".
Liverpool will resume their domestic schedule four players lighter following the October worldwide break.
Mane had begun the season in fine form, scoring four goals in the Premier League, and starting every game in all competitions thus far.
"People asked why this game was less intense".
"Together we decided that he would only play against Germany".
"You have to call the manager of any country and say can you leave players out and he says I am under pressure as well".
"Guys like Jordan only had two weeks after the World Cup".
Mignolet has featured just once for Liverpool this season, in the 2-1 Carabao Cup third round defeat to Chelsea.
Klopp has been a critic of the current worldwide schedule, offering a particularly scathing assessment of the Nations League, as he wants his players to enjoy some rest as the Reds look to challenge in the Premier League and Champions League.