The son of Galileo won four of his six starts as a juvenile, grabbing Group One glory in the National Stakes, and also passed the post in front in the Prix Jean-Luc Lagardere at Longhamp only to be subsequently disqualified for causing interference.
Gleneagles has been heavily supported for the season’s first Classic at Newmarket and O’Brien is delighted with his condition.
Speaking in a stable tour, the trainer said: “Everything seems fine with him so far. He’s a Galileo with a lot of speed and he doesn’t do much once he gets to the front, which is coming through from his pedigree as a lot of them were like that.
“He’s a full-sister to Marvellous, but he’s a much stronger traveller and pacier horse than she was. He would have had no problem winning over six furlongs last year if we’d asked him too and he has more than enough pace for a Guineas.
“You’d imagine he’ll get a mile and a quarter, but you couldn’t be sure he’ll get much further than that.
“He’ll go for a spin at the Curragh on Sunday and we’ll sit down and make a plan for him after that.”
O’Brien also revealed he sees impressive Vintage Stakes winner Highland Reel as a horse that “could go straight to the Guineas.”
The chief Derby hope for the yard appears to be John F Kennedy, while Ol’ Man River is another likely Classic candidate.
That pair are also bound for the Curragh this weekend.
“He (John F Kennedy) has done well over the winter and everything seems fine with him so far,” said O’Brien.
“He was very babyish in all of his three starts last year, even after his third start he was whinnying in the winner’s enclosure after the other horses went out of the ring.
“At this stage it looks like we’ll stay at home with him for his two trials in the Ballysax and the Derrinstown Stud Derby Trial.
“We think he has grown up mentally this year, but the fact he was so babyish last year means that it probably makes sense to keep him at home for his first couple of starts rather than pitching him in deep by travelling abroad early this season.
“Fast ground won’t be a problem, he has a big stride and plenty of speed. He will go to the Curragh on Sunday for a day away with the rest of them.
“Ol’ Man River is very good and is doing everything right so far. He’s always been a very mature horse that shows plenty of pace in his work and while we haven’t made any decisions yet, he could go the Guineas route.
“He’s a bit like Camelot in that he’s much pacier than the vast majority of the Montjeu’s we’ve had, which is making us think about the Guineas. He wouldn’t be certain to get the Derby trip.
“You’d imagine he’d travel around Epsom very strongly and you couldn’t be sure what’s going to happen from the two-furlong pole.
“We’ll bring him to the Curragh on Sunday and make our plans after that.”
O’Brien revealed Aloft and Archangel Raphael could slot into Derby trials in the spring, with the Lingfield Derby Trial nominated for the latter.
Dick Whittington, who won the Phoenix Stakes on his sixth juvenile start, could go down the French Guineas route.
Heading the three-year-old fillies’ division for the team is Found, who tops ante-post lists for both the 1000 Guineas and the Oaks after a brilliant display in Longchamp’s Prix Marcel Boussac.
However, O’Brien has warned a trip to Newmarket could be in doubt if fast conditions prevail on the Rowley Mile.
He said: “She had a bit of a temperature a few weeks ago, so we eased off her a little bit. She’s in good form now and will go to the Curragh for a little canter on Sunday.
“She’s in all the Classics and I think she’ll be quick enough for a mile, though Joseph (O’Brien) and Ryan (Moore) both think she’ll get a mile and a half.
“The one thing is that she’s a big filly and while I don’t think she wants soft ground, she does have a round enough action and you wouldn’t necessarily want to belt her off really fast ground at Newmarket this early in the season as she’s a filly you’d look forward to through the whole year.”
Qualify is another potential Guineas challenger.
She was last seen finishing a luckless eighth in the Breeders’ Cup Juvenile Fillies Turf.
“She’s a nice filly and we just weren’t riding her right until we dropped her in behind in the Weld Park Stakes,” said O’Brien.
“She loves fast ground and you’d imagine she’d get a mile and could even get a mile and a half in time.
“She’s a big strong galloping filly and those Fastnet Rocks get better with age. We always thought she could be a Group One filly and hopefully she’ll get there.
“She’ll go to the Curragh on Sunday for a spin and we’ll look at possibly starting her off in a Guineas trial with a view to running in the Newmarket 1000 Guineas.”
One of the yard’s more interesting older horses is Tapestry, who beat the top-class filly Taghrooda in last year’s Yorkshire Oaks.
O’Brien said: “She’s in good form and could possibly start back in something like the Tattersalls Gold Cup or the Coronation Stakes.
“A mile and a half is probably her trip, but she could well get away with a mile and a quarter.
“I think she’s done well from three to four, she’s put on plenty of weight and looks stronger and bigger so we’re looking forward to her running.”