Celtic defender Gary Caldwell has called for research into the effects of food supplements and energy drinks following the death of Phil O'Donnell.The Motherwell captain, 35, collapsed on the pitch during his side's 5-3 victory over Dundee United on Saturday. The results of the post mortem examination have not been made public but there has been a spate of deaths of young footballers, many of which due to heart failure. In 2003, Cameroon midfielder Marc-Vivien Foe died at the age of 28 after suffering a heart attack during the Confederations Cup semi-final against Colombia in Lyon. Last August, Spain international Antonio Puerta, 22, died after also suffering a heart attack in his club side Sevilla's 4-1 win against Getafe. As a mark of respect to the former Celtic and Sheffield Wednesday player, Motherwell's match with Hibernian scheduled for tomorrow has been called off as has Gretna versus St Mirren at Fir Park and the Old Firm clash at Parkhead. A distraught Caldwell questioned the way modern-day footballers are asked to re-fuel before and after games. He said: 'When I heard the news on Saturday night football did seem insignificant at that point. 'It does put football into the background and who wins leagues and who wins points does seem irrelevant at this time. 'We are all distraught and it's a hard time for everyone at the minute. 'I think everyone's thoughts are just with Phil's family and Motherwell as well. 'We are just thinking about his family and hopefully everyone can gather around them at this time. 'I have thought about it. You drink energy drinks, you take supplements and you do it to become a better player. 'But I think somebody has got to look into it and try to see if it does affect you.' Caldwell insists that O'Donnell's death has affected all footballers regardless of how close they were to the former Scotland international. He said: 'I didn't know him all that well. 'I obviously know boys at Motherwell who knew him and I have seen him on a few occasions. 'He just seemed like a really nice guy. He was always smiling and happy and it's tragic that he died so young. 'I spoke with Brian Kerr (O'Donnell's former team mate) on Saturday night who knew him very well and he was devastated. 'I spoke to Steven, my brother, who didn't really know him well either and it was a huge shock to everyone in the football world. 'It was just a sad day.'