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.”
Among those returning to training ahead of Saturday’s visit of Southampton were Philippe Coutinho and Roberto Firmino, back from Brazil duty at Wembley, while Simon Mignolet returned from the Belgium to join his Reds team-mates.
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 returned from action with Senegal on Tuesday, alongside Dejan Lovren after the centre-half helped Croatia secure World Cup qualification.
Left-back Andy Robertson was back in training on Monday following Scotland international duty.