Carlo Ancelotti has expressed uncertainty over his future at Chelsea by claiming he would not "want to train a team that is not in the Champions League". The club resumes its involvement in the competition on Tuesday with a last-16 tie against FC Copenhagen but, unless they win the final in May, they may not be involved next year given their struggles to secure a qualification place via the Premier League.

It is assumed Ancelotti would be sacked by the Chelsea owner, Roman Abramovich, were he not able to arrest the team's current malaise – the champions are currently fifth having won only five of their past 16 league fixtures – and also failed to claim their first ever Champions League title. But the Italian has now indicated that such a failure could persuade him personally that his time at Stamford Bridge had reached a natural end.

"We know the Premier League is now very tough for us but we want to play in the Champions League next year, it is the most important thing for everyone," said Ancelotti, who joined Chelsea from Milan in June 2009 and went on to win the league and FA Cup double in his first season. "I don't want to train a team that is not in the Champions League as for me it is the best competition in the world. But I am an optimist and I believe my team has the quality [to finish in the top four]."

Asked about the worst-case scenario of having to manage Chelsea in the Europa League next season, something Frank Lampard has described as a "disaster", Ancelotti added: "This is why it is important we arrive [in the top four] of the Premier League. It will be a fight, there are five teams, maybe six teams with Liverpool, who want this."

Chelsea still have to face Manchester United twice and Tottenham, who are currently two points ahead of them, once before the end of the season, not to mention a visit from Manchester City, who triumphed 4-2 at Stamford Bridge last season. Ahead of such stern tests Ancelotti will hope Fernando Torres recaptures the form that persuaded Chelsea to spend £50m on him last month.

The striker has done little to impress in his two matches since arriving from Liverpool, the most recent of which was Monday's goalless draw at Fulham, and there is a belief he and Didier Drogba cannot function together – the pair started together in Torres's debut against his former club earlier this month before the Spaniard started on his own at Craven Cottage. He was replaced by Drogba midway through the second half.

Ancelotti insists, however, the pair can form a formidable partnership. "He [Torres] is a striker like Didier but it is not right to say they are in competition, they are in collaboration," said Ancelotti. "They have to work together to help bring the team in the best position."

For now, Chelsea's focus returns to the FA Cup. They host Everton in a replay of their fourth-round tie with Ancelotti confirming Drogba will return to his starting line-up in place of Torres, who is cup-tied having featured for Liverpool at the third-round stage.

One man who will not feature, however, is David Luiz, the £21.3m signing from Benfica. Ancelotti confirmed that the defender would start against David Moyes's men having impressed on his debut against Fulham but then had to backtrack after it was revealed that Luiz was ineligible for selection having signed for Chelsea on 31 January. According to the Football Association, a player must be registered with his current club by 28 January to take part in the fourth round of the competition.

"Carlo had forgotten the rules," confirmed a Chelsea spokesman. "He was reminded of it by the club secretary and has amended his team for the Everton match." Paulo Ferreria will replace Luiz in central defence.