Andre Villas-Boas admits Chelsea's poor form in December has cost them any chance of winning the Premier League title race.
But the manager remains confident his position is not under threat despite his admission that his side's performances have fallen well short of expectations.
Villas-Boas's side sank to a 3-1 loss to Aston Villa - their third home league defeat of the season - extending their recent run to four games without a win.
The defeat meant they were unable to take advantage of Manchester United's defeat to Blackburn Rovers and Tottenham Hotspur's failure to beat Swansea City, and allowed Arsenal to leapfrog them into fourth place.
Villas-Boas - whose side face Wolves on January 2 - said it was frustrating that his side had not been able to pick up points in a month when other title contenders had been dropping them.
"It's disappointing on the fact that, in the last three fixtures, all the top teams have dropped points.
"We spoke about how December could have been decisive in the running of the league.
"From what is happening now, Arsenal made the most of a good December. Liverpool, too, in some way. The rest of the teams have struggled.
"All of them dropped points, but we couldn't make the most of it. It's difficult for us to be in perspective for league contention this year."
Villas-Boas, who was brought to the club at great expense by billionaire owner Roman Abramovich after a successful season with Porto, said that there were no hard luck stories regarding his side.
"There is no running away with excuses. What we regret more is that, from the last four games, we've lost a big opportunity to shorten the distance to the leaders.
"Massive opportunities lost. We would have been running for the title if we'd had a better December.
"I don't think the title is realistic. Our reality is a fourth place finish, but that is not good enough."
The 34-year-old, who began his coaching career with a year with the British Virgin Islands, said he could not comment on his future.
"Ask that question to the owner, but I have no other information on the contract."
Didier Drogba put Chelsea ahead with a first half penalty, his 150th goal for the club.
The striker celebrated by saluting all four stands, prompting suggestions he was saying goodbye before the January transfer window opens.
But Villas-Boas believes the striker was simply bidding farewell ahead of the African Cup of Nations - although the manager hopes to persuade the Ivory Coast FA to allow the player to face Portsmouth in next weekend's FA Cup tie.
Stephen Ireland levelled for Villa before Stiliyan Petrov and Darren Bent secured the win with two late goals.
Ireland had been spoken to by manager Alex McLeish after a picture was posted on Twitter of the midfielder apparently smoking a shisha pipe and drinking a large glass of wine.
But McLeish was delighted with the player's reaction.
"He must have caught everybody's eye today. He was excellent.
"I asked him to be an enforcer in midfield - closing down, harrying and pressing. He did it really well against Arsenal and did it extremely well for the whole game today.
"His reading of the game was reminiscent of his Manchester City form. He's got to take that forward. That's got to be the standard every game.
"It's his head. Sometimes you don't have the confidence. Marc Albrighton struggled with confidence for the first few weeks of the season, but it can turn like that."
McLeish has come in for criticism this season but admitted the win at Stamford Bridge was his best day as Villa manager.
"It's my most satisfying day so far, but I'm hoping there are many more to come.
"I'm a guy who perseveres, who gets back up after being knocked down pretty regularly. I'd like to maintain some stability in the club into the new year."