Chris Froome says his bid to hold all three Grand Tour titles concurrently is not "likely" after crashes hampered his first week in the Giro d'Italia.
The Team Sky rider wants to add the Giro to the Tour de France and La Vuelta crowns he won last year.
But he is two minutes 27 seconds behind race leader and fellow British rider Simon Yates of Mitchelton-Scott.
"It is a big gap," Froome told Team Sky's website. "I wouldn't say it's likely at this point."
However, he added: "Stranger things have happened. We've got some extremely tough racing coming and we've got a long time trial as well."
Aside from needing to make up ground on the pink jersey, Froome who is 11th, trails defending champion Tom Dumoulin (Team Sunweb) by one minute 49 seconds.
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Competing despite an ongoing anti-doping case - after being found to have double the allowed level of a legal asthma drug in his urine after a test at last year's Vuelta a Espana - Froome is hoping to become the first rider to do the Giro-Tour double since Marco Pantani in 1998.
That challenge has proved too much for the likes of Alberto Contador and Nairo Quintana in recent seasons and Froome has found his ambitions hampered by a series of crashes.
The 32-year-old fell before the opening time trial in Jerusalem and during stage eight on Saturday, and has put his indifferent form down to a training plan tailored to see him peak in the last week of the Giro in order to be in good shape for the Tour.
"I always came into the Giro with the plan of building into the race, with the bigger goal of doing the Giro d'Italia and going on to the Tour de France," he said.
"It was never my objective to arrive right at the beginning of the Giro absolutely firing on all cylinders because as we've seen in riders who've done that in the past, they reach July and just have nothing.
"I was always looking to build through this period, but I think the crash (before stage one) was a setback to me. I also think the second crash (during stage eight) didn't help, also on my right side, but we're here and that's the nature of cycling."