Giant's Causeway is unlikely to run again this season after his triumph in the Group One Prix de la Salamandre on very soft going at Longchamp on Saturday.

"The horse is home fine but he wants better ground and as he knows his job well that is probably it for the season," the colt's trainer Aidan O'Brien said yesterday. "Giant's Causeway would look a Guineas type and we will see where he fits in next spring."

O'Brien's Royal Kingdom is a possible for the Serpentine Gallery Royal Lodge Stakes at Ascot next weekend having been taken out of yesterday's Aga Khan Studs National Stakes because the horse was not fully fit. "Royal Kingdom could go to Ascot now," he said. "He did not eat up last night which is not like him and I wasn't 100 per cent happy when we cantered him this morning so we decided to take no chance with him."

O'Brien won his third major French juvenile prize of the season as Giant's Causeway stamped his class at Longchamp. The hotpot (5-3 on) made light of the puddinglike conditions by leading from the front in the Parisian feature.

Confidently ridden by Michael Kinane, the favourite was asked for his effort over two out and duly responded by quickening clear.

Race Leader, one of three British hopefuls in the race, put in a eye-catching finish but the Irish colt won by two lengths.

Kinane said: "Giant's Causeway is a like a bulldozer. He will simply handle anything."

However, he refused to drawn on comparisons with the unbeaten Prix Morny winner Fasliyev. "They are too different types altogether," he added.

O'Brien's previous big juvenile wins in France this term have been recorded by Rossini (Prix Robert Papin) and Fasliyev (Prix Morny).