Mr Singh has been ruled out of the Ladbrokes St Leger at Doncaster a week today.
The John Gosden-trained colt will miss the final Classic of the domestic Flat season after he returned a dirty scope.
Hugo Lascelles, racing manager for owner Lady Bamford, said: "It's a great, great shame but he won't be running in the Leger.
"He scoped dirty, unfortunately, and he just won't be ready in time."
Mr Singh had been around the 5-1 mark for the Leger after he excelled with a striking victory in the Bahrain Trophy at Newmarket in July.
His withdrawal is another blow for the great race after Sumbal was taken out of the equation earlier in the week by French trainer Francis Graffard.
Just 12 horses, including Mr Singh and Sumbal, were in the equation for the Leger, with six of those trained by Aidan O'Brien.
Connections of classy Goodwood winner Simple Verse have, however, not ruled out the possibility of supplementing the filly at a cost of £50,000 on Monday.
RICHARD HUGHES SET FOR FIRST RUNNER AS A TRAINER AT EPSOM
Richard Hughes is on the verge of saddling his first runner as a trainer at Epsom on Thursday.
The three-times champion jockey retired last month after a distinguished career and is ready to competitively take the plunge in his new vocation.
Hughes, 42, has entered former Charlie Hills inmate Castle Talbot, bought on behalf of owner Gerry Dolan for 15,000 guineas in July, in the Pinsent Masons Handicap over an extended mile.
Castle Talbot raced four times for Hills, twice finishing third in maidens at Lingfield and Newcastle, and is one of 22 horses in contention for the £12,000 Epsom handicap.
Hughes said: "I'm hoping to run him (Castle Talbot) and it will be good to get started.
"He's nice horse and needs a bit of cut in the ground - or at least I think he does.
"He's a grand horse and I'm hoping he goes well.
"It's been a very busy month - I'm completely up to my eyeballs at the moment - and we've got lots more trips to the sales to come in the autumn.
"Things are going grand, though, and I'm enjoying it."
JANE CHAPPLE-HYAM KEEN ON TRIP TO AUSTRALIA WITH ENERGIA DAVOS
Jane Chapple-Hyam is leaning towards an ambitious trip to Australia for a shot at the Emirates Stakes with Energia Davos following his last-gasp success in the Stella Artois Handicap at Ascot.
The seven-year-old made a winning start to life under the Newmarket handler following his sale out of Marco Botti's yard when wearing down his former stablemate Puissant in the final strides of the mile event to complete the final leg of a treble for winning rider Jamie Spencer.
Although his odds were trimmed from 33-1 to 20-1 for the Cambridgeshire by Paddy Power, Chapple-Hyam was quick to point out that the Group One mile handicap at Flemington on November 7 is likely to be the next target.
Chapple-Hyam said: "He would get in the Cambridgeshire, but you are forgetting that I am from Australia and there is the Emirates Stakes at Flemington, which is the Saturday after the Melbourne Cup.
"Jamie is in town, it is now up to the owner if he wants to pay the airfare.
"The quarantine for that starts on October 24, and the Cambridgeshire is on the 26th. We have got to make up our mind which race to go for, but we might just say 'yes' to Australia."
CHARMING THOUGHT RETURN PUT ON HOLD BY CHARLIE APPLEBY
Charming Thought has seen his comeback further delayed after being ruled out of making his seasonal return in the Park Stakes at Doncaster.
Trainer Charlie Appleby had earmarked the Group Two seven-furlong event at Town Moor on Saturday week as a potential starting point for the three-year-old.
The Group One winner has not been seen since defeating Ivawood in last year's Middle Park Stakes at Newmarket, after suffering an injury setback in his build up towards the Qipco 2000 Guineas.
Appleby said: "He has not come round in time for the Park Stakes, so he won't be going to Doncaster. We have Safety Check in there and he is heading towards that.
"We are still tapping away with him, but he is taking longer than we expected to get him back to where we want him. We have not singled out a race for him yet."
Although suffering an interrupted campaign this season, Appleby hopes he can make up for lost time after revealing the Oasis Dream colt will be kept in training next year.
Appleby said: "The main thing is that he is staying in training next season, which is good as we need to build up the four-year-old team.
"On physical evidence it is looking like sprinting is going to be his game, but we won't know that until he gets to the racecourse."
JOHNNY MURTAGH EAGER FOR DONCASTER LEGENDS CHALLENGE
Johnny Murtagh is relishing the prospect of lining up alongside Tony McCoy in the Clipper Logistics Legends Classified Stakes at Doncaster next week.
The straight-mile contests sees 16 former jockeys returning to the saddle in aid of the Northern Racing College and the Injured Jockeys Fund's Jack Berry House.
Murtagh, a five-time champion jockey on the Flat, and 20-time champion jump jockey McCoy are the star names in a field that also includes Jim Culloty, Kevin Darley and At The Races broadcaster Luke Harvey.
Murtagh, who retired in February, 2014, and now trains on the Curragh, said: "I am really looking forward to the Legends race next week.
"Dale (Gibson) asked me to do it last year but I couldn't, although I said I would definitely do it this year so when he rang me I was happy to be involved.
"I ride out five lots and muck out six horses a day, so I am still pretty fit. I just hope I am given a nice draw on a horse with a decent chance.
"It would be great to be involved in a driving finish with AP (McCoy), just to see how good he really is!
"Also Luke Harvey has been doing a lot of talking on Twitter! I'm looking forward to seeing how he gets on."
IRISH CHAMPIONS WEEKEND OPTIONS FOR PANAMA HAT
Panama Hat will be left in both the Palmerstown House Estate Irish St Leger and the KPMG Enterprise Stakes on Irish Champions Weekend at the confirmation stage.
Connections are favouring the Group One St Leger on the back of his brave effort at Arlington last time out when worn down close home in the American version.
"We're still leaning towards the Leger with him," said trainer Andy Oliver.
"As yet we haven't had a final chat with the owners and he'll be left in both at the five-day stage.
"He took the whole trip to America remarkably well. I can't see an obvious winner of the Leger, so it could be worth having a go.
"I think it will cut up to quite a small field and then you're looking at three or four main contenders and on ratings we don't have much to find.
"We're up to 111 now and that puts him right in the mix.
"It's a nice position to be in, but on the other hand you don't want to make the wrong decision."