Chaparral heads challenge High Chaparral will be the flagship runner in an extensive Irish challenge for this week`s Group One bonanza.The Prix de l`Arc de Triomphe is the main focus of a week that contains a remarkable eight Group One races between Longchamp and Newmarket. Aidan O`Brien yesterday conceded that a long break since High Chaparral`s Irish Derby success, and a bout of the cough, has been a less than ideal preparation for the colt`s likely Arc clash on Sunday with the French Derby hero Sulamnai. However, before that, O`Brien`s focus will be on Newmarket and a possible return to action for Hold That Tiger in Thursday`s Middle Park Stakes. The former 2,000 Guineas favourite hasn`t run since finishing unplaced behind his stable companion Spartacus in the Phoenix Stakes in August. Both colts figure among the contenders for both the Middle Park and Sunday`s Grand Criterium. 'Hold That Tiger has been back in work and it`s possible he will run in one of them. We will have more of an idea about who goes where on Tuesday,' O`Brien said yesterday. Friday`s Cheveley Park Stakes features the Jim Bolger pair Danaskaya and Luminata among its entries but O`Brien`s juvenile filly focus is more likely to be on the Prix Marcel Bousssac. 'We have Yesterday and Miss Helga in the Boussac and they are possible runners,' said O`Brien. Yesterday finished a length and a half off Rainbows For All in the Debutante Stakes in August and that Kevin Prendergast-trained filly is also a likely Boussac runner. However, Prendergast`s main concern yesterday was the absence of recent rain at Longchamp for the Prix de l`Opera hope Rebelline. 'She is on target for the race if we get rain. We`re hearing it`s quite dry over there but we are still hoping for the ground to get a little more easy. Good to yielding would be ideal,' Prendergast said. 'Rainbows For All is in the Boussac and I`ve also got Minashki in the Prix de l`Abbaye,' he added. In contrast, Dermot Weld is concerned about the Longchamp authorities possibly over-watering the track before the weekend. 'Our running plans will depend on the weather. Agnetha will run in the Abbaye if its good to firm; if it`s soft Tiger Royal will run.' Irresistible Jewel will go for the Prix de l`Opera if its good or good to firm. But we can`t make out minds up until later in the week. 'It`s dry at Longchamp now but I just hope they don`t over-water,' said Weld. The Curragh trainer is also planning the send the double Group Three winner Dress To Thrill to Newmarket on Saturday for the Sun Chariot Stakes. Aidan O`Brien also reported yesterday that his runners at Ascot on Saturday returned home unscathed and didn`t rule out another appearance this season for the Royal Lodge third Van Nistelrooy. 'We will have to see how he is once he starts cantering again but it`s possible he could have another race,' he said.