Derby favourite Yeats undergoing physio on muscle problem. Aidan O´Brien has reported that his long-time Epsom Derby favourite Yeats is undergoing daily treatment on a muscle problem he developed following a work-out at Ballydoyle on May 21.The unbeaten son of Sadler´s Wells is now avaliable as the 11/4 joint favourite for the race, having drifted from 9/4. He now shares favouritism with the Godolphin-trained Snow Ridge, with O´Brien stating 'physiotherapist Liz Kent has been treating Yeats every day since he tweaked a muscle.'However, he added 'it seems to be a case of so far so good with the horse at the moment.'Physiotherapist Kent has previously treated equine stars such as Alamshar and Beef Or Salmon.