PARIS &ndash; Aidan O&rsquo;Brien has made the surprise move of naming Christophe Soumillon to ride Irish Champion Stakes winner Cape Blanco in the Prix de l&rsquo;Arc de Triomphe at Longchamp on Sunday.\r\nSoumillon, a native of Belgium, won the Arc in 2003 with Dalakhani and in 2008 with Zarkava when he was first-string rider for the Aga Khan but was apparently left without a mount in this year&rsquo;s race until O&rsquo;Brien came to the rescue.\r\nCape Blanco had been ridden by Johnny Murtagh to win the Irish Derby. It was Colm O&rsquo;Donoghue on board for his second-place finish to Harbinger in the King George VI and Queen Elizabeth Stakes. In his Irish Champion triumph, Jamie Heffernan was at the controls.\r\nWith Murtagh having chosen to ride Fame and Glory in the Arc, O&rsquo;Brien has gone to Soumillon for Cape Blanco. O&rsquo;Brien has teamed up once before with Soumillon, that when Dylan Thomas won the Group 1 Prix Ganay in 2007.\r\nA large field is expected to line up for the Arc as 23 horses remained in the race on Wednesday morning with two more expected to be supplemented on Thursday. They would be Grand Prix de Deauville winner Marinous and Lope de Vega, the winner of both the Poule d&rsquo;Essai des Poulains (French 2000 Guineas) and the Prix du Jockey-Club (French Derby) who has gone badly off form since then and would be making his first start at 1 1/2 miles.\r\nSarafina, trained by Alain de Royer-Dupre to win this year&rsquo;s Poule d&rsquo;Essai des Pouliches (French 1000 Guineas) and the Prix de Diane (French Oaks), worked Tuesday morning over the Les Aigles training strip at Chantilly. She went nine furlongs and was not given a hard time of it as Royer-Dupre explained that this was the first time she had ever worked on heavy ground. As a result, he termed her work as &ldquo;not overly demonstrative.&rdquo;\r\nThe ground remained soft at Longchamp on Wednesday morning. Weather forecasts now differ but all of them predict some rain at least on Thursday and Friday, so prediction for the going at Longchamp on both Saturday, when four Group 2 races, among them the one-mile Prix Daniel Wildenstein, and the 1 1/8-mile, 155-yard Prix Dollar, will be run, and on Sunday, when the Arc headlines a card of seven Group 1 contests, the most ever run at a European track on a single day.