Jose Mourinho believes referee Chris Foy's performance in the defeat at Aston Villa could cost Chelsea the title.
Premier League leaders Chelsea, who play Crystal Palace on Saturday, lost 1-0 at Villa Park in a match which saw Mourinho sent to the stands following the dismissals of Willian and Ramires.
Mourinho maintains Manchester City are title favourites and Liverpool have a strong chance, while he refused to rule out Arsenal despite hammering the Gunners 6-0 last weekend.
If the Blues are beaten by one or two points in the title race, Mourinho will look no further than this month's defeat at Aston Villa, which still leaves him seething at the performance of referee Foy.
Asked if the Villa match could be pinpointed as costly come the end of the season, Mourinho said: "Yes, because the other matches we lost because we didn't play well, because the opponent was better than us, because we missed big chances.
"If you go to the other matches you find the natural reasons for losing a match, if you go to the Villa match it's difficult.
"What happened in the defeat against Villa I never learn, I never accept.
"Somebody was very successful in putting a hurdle in front of us. And we crashed the hurdle against Aston Villa and we lost.
"Villa was not a normal football match and we always hope that football matches are normal."
Mourinho will face a personal Football Association disciplinary hearing at the end of next week to challenge his improper conduct charge issued following his dismissal at Villa.
"If you lose in the right way you have to move on and try not to lose again," said Mourinho, who faces a £10,000 fine for his second sending-off of the season.
"The only thing I didn't learn is to lose with that kind of referee performance, because it's not a mistake, it's a performance.
"I learn to control my emotions and I learn to calm down in the moment like I did, but I don't learn how to accept that kind of performance."
Chelsea responded to the Villa loss by beating Galatasaray - and then Arsenal - in a contest which took them into the Champions League quarter-finals.
Paris St Germain are Chelsea's opponents in the last-eight first leg next Wednesday and this week have made overtures towards Blues forwards Eden Hazard and Oscar.
Former Newcastle midfielder Yohan Cabaye this week expressed his hope to be reunited with his former Lille team-mate Hazard, while Lucas Moura thinks PSG should move for his Brazil team-mate Oscar.
In an era of UEFA's Financial Fair Play regulations, PSG should not be able to consider signing the playmaking pair, according to Mourinho, who believes the astronomical spending of the likes of Manchester City, PSG, Monaco and others should be scrutinised by the footballing authorities.
However, if FFP is not applied to PSG, Mourinho suggested the pair could be sold - at a price.
Mourinho said: "No. It's not irritating. No problem.
"If there is Financial Fair Play, they don't have money to buy them.
"If there is no Financial Fair Play and they threw something crazy, £300million for both, I think Chelsea has to think about it."
French journalists were present for the media conference and Mourinho asked his inquisitors if they were from Canal+, a reference to unguarded comments made about Samuel Eto'o's age which the broadcaster made public.
Eto'o is out with a hamstring injury for Chelsea's trip to Selhurst Park to play a Crystal Palace side fighting for their top-flight status.
Chelsea's priorities are at the other end of the standings, with confidence restored following the thrashing of Arsenal, which featured another controversial refereeing decision as Andre Marriner mistakenly sent off Kieran Gibbs for an offence committed by Alex Oxlade-Chamberlain.
Neither served a suspension as the dismissal was retrospectively applied to Oxlade-Chamberlain and Arsenal's appeal was successful as the ball was going wide when he handled the ball in making a diving save.
Mourinho accepted Marriner's human error, but declined to answer when asked about Oxlade-Chamberlain being cleared.
"I prefer to laugh," Mourinho said.
"You think if Oxlade thinks the ball goes out he dives for that ball?"
Chelsea are unbeaten in nine London derbies in the league this season, with six wins.
"This one is the last one so let's try to make it without defeat in the London derbies," added Mourinho, whose Blues beat Palace 2-1 in December.
"For the fans 4-0 against Tottenham is more than three points, 6-0 against Arsenal is more than three points.
"We are in a good run, we are in a good moment. We are enjoying the situation.
"Palace was difficult at home and when Pulis was there for about two weeks, he was just arriving. Now after months of work and matches and matches, they are much more Tony Pulis' team and it's going to be very difficult."
Source: PA
