Following their worst league run for almost 15 years, the champions are 10 points behind leader Manchester United and Ancelotti believes it could be too late to return to the top.
"At this moment we have less possibility to win the Premier League because it is less simple to close this gap," Ancelotti said. "In the FA Cup and Champions League we have more possibility."
But there are signs that Chelsea's season is getting back on track following three straight victories in all competitions, a stretch in which the team scored 13 times without conceding.
"The moment is very good, we played very well against Bolton (winning 4-0 on Monday) and we want to continue this," Ancelotti said. "Our atmosphere has totally changed compared to one month ago."
Chelsea was held last month to a 1-1 draw in the league by Everton, which has proved to be a stubborn opponent at times this season. Arsenal is the only team in the top seven to have beaten Everton so far.
But Everton manager David Moyes isn't dismissing the threat posed by Chelsea on Saturday.
"When they got an opportunity they took it and defensively they were terrific (at Bolton)," Moyes said. "I have seen them playing more fluent football in times gone past but they were very efficient.
"When you have people who can win games out of nothing like (Didier) Drogba, (Nicolas) Anelka or (Florent) Malouda and defenders who can deal with physicality and keep it calm like John Terry, (Branislav) Ivanovic and the goalkeeper (Petr Cech) - you have the makings of a really good side."
Ancelotti resisted questions Friday about Chelsea's bid for Liverpool striker Fernando Torres being rejected.
"He is not my player and I have to have respect for Liverpool," Ancelotti said. "I am happy because the club is doing a fantastic job in this transfer market. The club is trying to do everything to improve the squad."
Chelsea's hopes of signing Brazil defender David Luiz from Benfica before the transfer window closes Monday appear to be fading.
"Negotiations between Benfica and Chelsea FC, with a view to the possible transfer of David Luiz, were concluded today without the parties having reached an agreement," the Portuguese club said in a statement Friday.
In another of Saturday's fourth-round matches, Manchester United travels to third-tier club Southampton, where goalkeeper Anders Lindegaard could make his debut for the Premier League leaders.
"We picked up one or two bruises at Blackpool the other night - it was quite a physical game, but we'll still take a strong squad (to Southampton) because it won't be an easy match - away games in cup ties never are," United manager Alex Ferguson said. "I went to see Southampton play Oldham earlier this month and they won 6-0. They're having a good season. They play good football and I'm sure they'll have a go."
"These are the games that the club wants and it's where we need to be again, playing against the Manchester Uniteds, the Chelseas, and the Tottenhams," Chaplow said. "It's where the club used to be and where it's striving to be again, so it will be nice to welcome Manchester United to St. Mary's once more, and hopefully we can put on a good performance and give the fans something to cheer about."
Arsenal, second in the Premier League, are also facing a League One - Huddersfield - on Sunday.
Also Sunday, Manchester City will be without winger Adam Johnson against Notts County, West Ham will be looking for a distraction from its relegation battle when it hosts Nottingham Forest, Tottenham travels across London to Fulham and Wolverhampton plays Stoke.
Saturday's other fourth-round fixtures are: Aston Villa vs. Blackburn; Birmingham vs. Coventry; Bolton vs. Wigan; Burnley vs. Burton Albion; Sheffield Wednesday vs. Hereford; Stevenage vs. Reading; Swansea vs. Leyton Orient; Torquay vs. Crawley Town; and Watford vs. Brighton.
