Young athletes have been warned not to ignore the symptoms of heart problems or head injuries after the death of Phil O'Donnell, one of Scotland's best-known professional footballers. 

Alex Salmond, the Scottish First Minister, led tributes yesterday to the Motherwell captain, who collapsed in the 72nd minute of Saturday's game against Dundee United.  He was 35, and married with four children.  The cause of his death has not been confirmed. 

"The circumstances of his death are obviously a huge blow to Scottish football.  He was a model professional who was popular among fans and fellows players," Mrs Salmond said. 

Jack McConnell, who represents Motherwell in the Scottish Parliament, also praised the midfielder who, he said, helped to transform the team.  The former Scotland manager Craig Brown said: "You would not get a more ideal role model for a young footballer than Phil O'Donnell.  I think in his first spell at Motherwell he was probably the best box-to-box mid-field player - maybe not just in Scotland but in the UK." 

Mark McGhee, the team manager, said it had been an honour to work with such a "great, great player." 

He added: "We're going to miss a guy who was a fine man, a guy who was a fantastic example to all of his colleagues.  He was a man among boys in his attitude and professionalism." 

O'Donnell joins a long list of professional footballers who have died suddenly, despite regular heart checks. 

Specialists have warned that the fact that top-class athletes are so accustomed to pushing their bodies may blind them to the early signs of seizures or heart attacks. 

The problem of heart failure was underlined by two shocking cases in quick succession over the summer.  On 25 August, the Sevilla midfielder Antonio Puerta collapsed 35 minutes in to a match.  He died three days later from cardiac arrest.  On the day he died, Clive Clarke, a 27-year-old Leicester City defender, collapsed during a match against Nottingham City.  He survived. 

A month later, the New York-based Journal of Athletic Training issued a warning to footballers after one teenager ignored three bangs to the head, but on the fourth was treated for concussion.  Over the next two years, he ceased growing normally, and was diagnosed with hypopituitarism, a hormone deficiency that causes excessive tiredness and muscle weakness, which doctors ascribed to his football injuries. 

The Journal said athletes were "notoriously poor" at reporting symptoms of injury, and warned: "Mild traumatic brain injuries, (including) concussions, are prevalent among young athletes.  These injuries often have more serious consequences than previously thought." 

The charity Cardiac Risk in the Young (CRY) recently launched a programme to screen 1,500 athletes.  These checks are now routine for football players in the elite leagues, but away from the big money, young athletes are still at risk of sudden death from heart problems. 

Alison Cox, CRY's chief executive and a former Wimbledon player, warned: "Often people relate pains to over exertion, or a drop in power to 'an off day', but sometimes these are the body's warning signs of heart conditions."

Other football fatalities

ANTONIO PUERTA

The Sevilla midfielder, aged 22, died in August after suffering a heart attack during a match with Getafe.  The Spanish international collapsed in the 35th minute of the game.  Medics resuscitated him but he collapsed again in the changing rooms.  He died three days later.

MIKLOS FEHER

The Hungarian international, 24, died of a heart attack in January 2004 while playing for Benfica in a Portuguese league game against Vitoria SC.  The centre-forward collapsed in injury time after receiving a yellow card.  He was taken to hospital but died two hours later.

MARC-VIVIEN FOE

The ex-West Ham United and Manchester City midfielder, 28, died while playing for Cameroon in the Confederations Cup in June 2003.  He fell to the ground in the 72nd minutes of the game.  An autopsy revealed he died of a heart attack caused by an enlarged right ventricle.