Sinndar has been raised 4lb to 132 in the ratings following his sparkling performance in winning the Prix de l'Arc de Triomphe Lucien Barriere at Longchamp on Sunday.
John Oxx's star colt, also winner of the English and Irish Derbys, beat Egyptband by one and a half lengths, with Volvoreta three lengths adrift in third place.
Senior British handicapper Nigel Gray said yesterday: "I have discussed the race with my colleagues in Ireland, Geoffrey Gibbs and Garry O'Gorman, and it is interesting to note that Sinndar went into this year's Arc with a similar record and the same rating of 128 as did Montjeu before he won the race last year.
"We have decided to raise Sinndar to 132, though the French senior handicapper Geralde Sauque rates him 1lb higher, but of course the International Classifications meeting at Hanover in December will decide the final figures."
Gray went on: "It is a great shame Montjeu was not able to show his true form, if he had he may have pushed Sinndar to a higher rating than 132 - he may be capable of a higher performance but so far he has not needed to."
Montjeu ended last season on a mark of 135 and reflecting on the John Hammond-trained colt's form this year, Gray went on: "His best performance this year I think was in the King George at Ascot where we had him on 129, but he did win so easily."
Sinndar's Arc performance was the fourth best in the race since 1990, Peintre Celebre taking top billing on 137 in 1997, followed by Suave Dancer on 136 in 1991 and Helissio on 134 in 1996.
Meanwhile, Sinndar returned home to the Curragh on Sunday night in good heart and will not run again this season, but his long-term future is still undecided.
He was accompanied on the journey from Longchamp by stable companions Namid, who won the Prix de l'Abbaye, and Mouramara, who started the weekend off in great style for Oxx when winning Saturday's Prix Royallieu at the same course.
All three are owned by the Aga Khan and Oxx said yesterday: "They came back late last night, but they travelled well and have all eaten up so it is a bonus that they are all right."
There is no doubt that Oxx would love Sinndar to stay in training next year, but he added: "No decision has been made yet and there are obviously plenty of other considerations than those of the trainer!
"The Arc is a race everyone wants to win and it good for a three-year-old to prove himself against older horses and add it to his two Derby wins."
It seems unlikely that Namid and Mouramara will run again this season either, but Oxx went on: "There is a valuable race in Hong Kong later on, but is has been great to win a l'Abbaye with Namid after having surgery on a knee in June, so he may have done enough for now.
"The Prix Royal-Oak (at Longchamp on October 22nd) may be a possibility for Mouramara if the ground was not too heavy for her - she is a good filly and we will have to see."
