Jurgen Klopp underwent a successful operation to remove his appendix shortly before Liverpool surrendered a two-goal lead to draw with Sunderland.
The German was taken ill on Friday night and club doctor Andy Massey diagnosed appendix problems on Saturday, after which he was driven to hospital and had surgery about 1.30pm.
Klopp was informed of his side’s result – a 2-2 draw at home to Sunderland having squandered a two-goal lead with nine minutes remaining – after his operation at Aintree Hospital.
First-team duties were undertaken by the remaining members of his backroom team, including assistant coaches Zelkjo Buvac and Peter Krawietz, first-team development coach Pepijn Lijnders and goalkeeping coach John Achterberg.
Liverpool have an FA Cup fourth round replay at West Ham on Tuesday but it is not yet known how long Klopp will be unavailable for.
In Klopp’s absence, first-team development coach Pepijn Lijnders was disappointed with the manner of the Reds’ collapse on a day around 10,000 fans walked out to protest against ticket prices.
“In the last 10 minutes we dropped off too much and let them play longer balls,” he told the BBC.
“We felt that we were in control of the game and you see that one moment changes everything.
“There are still eight to 10 minutes where you have to be calm and play, keep moving the ball into the final third, so when you lose it you can counter-press and stay higher up the pitch.”