Aidan O'Brien's Montjeu colt was unbeaten in three starts as a juvenile and a devastating display in the Racing Post Trophy at Doncaster catapulted him to the head of the betting for both the Guineas and the Derby.
However, Fallon, able to form an unbiased view as he currently has no ride in the season's first Classic, feels the quicker ground St Nicholas Abbey will encounter this weekend leaves a question mark over his chances.
The six-times champion jockey, who has ridden four 2000 Guineas winners, said: "I was very impressed with Elusive Pimpernel, who clocked a very good speed figure in the Craven Stakes. He's proven he can come down the hill and has won on fast ground.
"The Coolmore horse (St Nicholas Abbey) beat Elusive Pimpernel easily in the Racing Post Trophy but the ground was soft that day and this weekend it will be fast. Will St Nicholas Abbey be as effective on fast ground? If he can handle the fast, then he will be a freak." St Nicholas Abbey is one of three possible runners for O'Brien, who could also saddle Fencing Master and Viscount Nelson in his search for a sixth 2000 Guineas winner.
Olivier Peslier looks set to be given the green light to ride Hearts Of Fire in the race.
The French jockey partnered Pat Eddery's colt to three juvenile successes but there had been some doubt about his Newmarket availability due to his commitments to the Wertheimer brothers.
Setsuko was poised to represent the powerful owners in Saturday's Kentucky Derby, but is unlikely to make the cut for the Churchill Downs feature, freeing up Peslier for the trip to Headquarters.
That will be welcome news for Eddery, who has been delighted with his colt's recent homework and had arranged for Stephane Pasquier to take the ride had Peslier been forced to miss out.
"He's been working well and goes there with a sporting chance," said the trainer.
The Sheikh Hamdan Al Maktoum-owned Awzaan is one of only a handful of previous Group 1 winners in the race.
Although Mark Johnston's Middle Park Stakes winner has yet to go beyond six furlongs in competitive action, the owner's racing manager Angus Gold is confident the step up to a mile will not be beyond him. "He improved all through his juvenile season and although he has yet to race beyond six furlongs, I do not see the mile being a problem," said Gold. "If he had not shown so much speed through last season, nobody would question his ability to stay.
"He has a good attitude and as he showed when he galloped at Newmarket, he switched off and quickened up well."
Clive Cox's Xtension is set for his first appearance since finishing third in last season's Dewhurst Stakes and the trainer is confident of a bold show.
"He's in good nick and we just need to get him through this week in one piece," said Cox.
Richard Hannon has a strong hand with Greenham Stakes first and second Dick Turpin and Canford Cliffs both set to line-up. The Godolphin team have not tasted 2000 Guineas success since Island Sands struck in 1999 but they have a strong hand with Saeed bin Suroor's Al Zir and Poet's Voice, as well as Mahmood Al Zarooni's Buzzword in the mix.
John Best is set to run both Inler and Elspeth's Boy, while the Mikel Delzangles-trained Makfi is the sole French challenger.