Mr Barrymore is staying at the Marchwood Priory in Southampton, which is commonly used by celebrities battling addictions and depression.
A spokesman for the Priory said: "I can confirm that he has checked in following the events on Saturday morning. He has been treated here before.
"I can't confirm what he is being treated for, but he is under a considerable amount of stress after the last 24 hours or so."
The comedian's agent Ann Chudleigh said: "Michael is deeply saddened by this terrible tragedy. At the moment his concern and thoughts are for the young man's family."
Police have named the dead man as Stuart Lubbock, 31, a wholesale butcher's supervisor, from Harlow, Essex.
He was discovered unconscious in the pool of Mr Barrymore's house in Roydon, near Harlow, just before 0600BST on Saturday morning.
Police said post-mortem tests had shown that Mr Lubbock died from drowning. Further toxicology tests are being carried out.
Until further tests are carried out - which are expected to take several weeks - Essex Police cannot say whether the death is suspicious or not.
'Pleasant and sociable'
Neighbours described him as a "pleasant, sociable" man who lived with his father, Terry and brother Kevin in a terrace house in Great Brays, Harlow.
He is believed to have a daughter aged two, but had split from the mother of his child.
Mr Lubbock had been found unconscious in the swimming pool wearing only his boxer shorts.
He was taken to the Princess Alexandra Hospital in Harlow, but died two hours later despite efforts to revive him.
Taxi journey
He had arrived at the celebrity's house at about 0230BST after a night at the Millennium Club in Harlow.
Norman Hicks, of Essex Police, said: "At some stage he appears to have decided to go for a swim on his own."
Cab driver Keith Herrett said he took Barrymore and three other people back to the house from a Harlow nightclub just hours before the young man was found unconscious in the pool.
Mr Herrett, 40, office manager with cab firm Ace Apollo, said Mr Barrymore regularly used the firm.
"He is a regular in Harlow. Basically, he goes where he wants to go. I have been in the post office in Roydon and seen him go behind the counter and start serving. He's just that kind of bloke."
Mr Barrymore is famous for his distinctive presenting style on hit shows including Strike It Lucky and My Kind Of People.