Footballer Phil O'Donnell died of heart failure, his club said tonight.

The Motherwell captain collapsed as he was substituted during his side's 5-3 defeat of Dundee United on Saturday.

He was rushed to hospital after apparently suffering a seizure, but he did not regain consciousness.

In a statement released by Motherwell tonight Dr Robert Liddle, the club doctor, said: "The post mortem revealed that Phil had suffered left ventricular failure of the heart."

O'Donnell, who was married with four children, was the latest of several professionals and promising youth footballers around the world to die during matches or while training.

Fifa, the international governing body of football, said in August they were considering introducing cardiac testing of players.

O'Donnell made his debut for Motherwell as a 17-year-old and made just one international appearance for Scotland, against Switzerland.

He moved to Celtic in the 1994-95 season, playing over 100 games in five years, before moving to Sheffield Wednesday. He then returned to Motherwell.

The Old Firm game between Celtic and Rangers on Wednesday has been postponed as a mark of respect for Phil O'Donnell.