Leipzig are the surprise leaders in the Bundesliga approaching the midway point in the campaign, with Ralph Hasenhuttl's men having taken the top flight by storm following their promotion last season.
The Bulls are three points clear of Bayern Munich heading into the weekend, with the reigning champions still looking to get into their stride after a stuttering start to life under Ancelotti.
The former Real Madrid boss has now warned his squad not to expect Leipzig to just fall away and hand his team the title, claiming they can sustain a challenge.
"Leipzig are a very good team and have started very well into the season. I'm sure they'll be a big opponent until the end of the season," he said.
The Bavarians' early struggles have lead to Ancelotti coming under pressure although the Italian is not feeling the heat.
He brushed off concerns that Bayern need to go into the winter break as top dogs in the Bundesliga, claiming it is not essential to be crowned 'winter champions' if the title is going to return to Munich.
"The important thing is to be at the top of the table at the end of the season and win the title," he added. "In my last season in Madrid, we won 22 games in a row from September to December, but in the end we were not champions."