Newcastle manager Joe Kinnear was hospitalized on Saturday after falling ill while preparing for a Premier League match at West Bromwich Albion.
"After being examined by the club's medical staff, Joe was taken to hospital, as a precautionary measure, where he remains under observation," the club said in a statement.
No details of the illness were revealed.
Assistant manager Chris Hughton was to take charge of the Magpies for their game on Saturday afternoon.
Kinnear, 62, suffered a mild heart attack in March 1999 during his time as Wimbledon manager and later stood down from his post because of ill-health. He went on to manage Luton and Nottingham Forest, but then spent four years out of the game. The former Tottenham and Republic of Ireland defender was appointed as interim manager at Newcastle in September last year in the wake of Kevin Keegan's resignation and admitted his earlier efforts to return to the game had been hampered by concerns over his health.
Newcastle owner Mike Ashley extended Kinnear's initial rolling monthly contract to the end of the season. A two-year deal has been offered, but Kinnear is apparently delaying signing it until Newcastle's Premier League status is secured.
His stint has proved eventful, bringing him three Football Association charges he admitted one, a second was found "not proved" and the third is outstanding as well as an extensive injury list and frustration during the recent transfer window. Newcastle lost goalkeeper Shay Given and midfielder Charles N'Zogbia to Manchester City and Wigan respectively, and were only able to recruit Kevin Nolan, Ryan Taylor and Peter Lovenkrands despite Kinnear's hopes of adding "four or five" players.