Everest winner Think About It has returned an elevated white blood cell count during routine testing and is in doubt for the Group 1 George Ryder Stakes at Rosehill.

Trainer Joe Pride notified Racing NSW stewards of the results on Thursday but said a subsequent endoscopic examination came back clear.

With the horse showing no obvious signs of illness, Pride plans to conduct further blood tests on Think About It before deciding whether he will line up on Saturday.

The gelding is the pre-post favourite for the George Ryder Stakes (1500m) and his withdrawal would prompt a major reshuffle of the market.

It would also be a bitter blow for connections as the race is slated to be Think About It's final lead-up to the Doncaster Mile a fortnight from Saturday and an important test of his credentials as a miler.

Before the setback, Pride was bullish about the five-year-old's chances, despite an outside draw in barrier 17.

The horse was beaten as a short-priced favourite in the Canterbury Stakes (1300m) first-up when he had a tough run after drifting back early then making a mid-race move and sustaining a long run to the line.

Pride thought Think About It did an enormous job to hold on for second under the circumstances.

"If he had one of those graphs on a video game with the little carrots, he had five carrots and he'd spent four of them before the furlong," Pride said.

"He was on empty for that last bit but he's very brave and very tough and he kept going as best he could."

If Think About It does take his place on Saturday, Pride is banking on the horse's class to overcome his wide draw and says he will be given a positive ride in the bumper field of 19 runners.

"He led and won a Liverpool City Cup, so we'll be very positive on him on Saturday," Pride said.

"It's an extremely important run again for him this weekend in a race where we're trying to get a guide as to how strong he's going to be at a mile."

Think About It remained a $3.80 favourite for the George Ryder Stakes following news of his blood test results on Thursday, ahead of three-year-olds Militarize ($5) and Encap ($8.50).

He is also an equal $5 elect for the Doncaster Mile (1600m), sharing the top line of betting with Randwick Guineas winner Celestial Legend.