Liverpool manager Jurgen Klopp missed training on Wednesday after feeling unwell and admitting himself to hospital.
Klopp had undergone checks by medical staff and was due to be released in the evening so would not require an overnight stay.
The full Liverpool squad returned to Melwood from international duty to train late on Wednesday afternoon but it was without the German, who by then was already at hospital.
He is being assessed by doctors and will be absent from training on Wednesday as a result, said a statement from Liverpool.
There are currently no plans for Jurgen to remain in hospital beyond his appointment and he will therefore return home this evening; however, he may require further check-ups in the coming days.
The club urges that the privacy of Jurgen, his family and other patients is respected while attending hospital visits.
The Reds welcome Southampton on Saturday but there is no indication yet when Klopp, who is scheduled to face the media on Friday for his pre-match news conference, will return to training or whether he will be in charge for the Anfield fixture.
The 50-year-old, who last week made a trip to South Africa for a charity event, has missed a game before back in February 2016 at home to Sunderland, when he spent a short spell in hospital after suffering appendicitis.
On that occasion assistants Peter Krawietz and Zeljko Buvac oversaw the team’s 2-2 draw and they, plus coach Pepijn Lijnders, took training in the manager’s absence.
Among those who were back at Melwood were Philippe Coutinho and Roberto Firmino, back from Brazil duty at Wembley, while Simon Mignolet returned from Belgium to join his club-mates.
Captain Jordan Henderson also returned to full training after recovering from a thigh injury which forced him to miss the 4-1 win over West Ham before the international break and pull out of England’s friendlies against Germany and Brazil.
Dominic Solanke, Joe Gomez and Trent Alexander-Arnold arrived back after representing England at senior and U21 level respectively, with Ben Woodburn and Danny Ward also returning following their inclusion in the senior Wales squad.
Forward Sadio Mane also returned from action with Senegal on Tuesday, alongside Dejan Lovren after the centre-half helped Croatia secure World Cup qualification and midfielder Adam Lallana played in a behind-closed-doors friendly.
Left-back Andy Robertson was back on Monday following Scotland international duty.