Real Madrid manager Carlo Ancelotti believes his side won't secure a top-eight finish in the 36-team Champions League table and will have to go through a two-legged knockout playoff round for a chance to reach the last 16.

Off the back of a fabulous campaign in which they won record-extending titles in LaLiga and the Champions League, Real have struggle in their European title defence, losing three of their last four continental matches.

With six points after five games, Real are languishing four points off the top eight in 24th, the last spot that earns a place in the playoffs, as they brace for a visit to in-form Atalanta on Tuesday.

The Serie A leaders are fifth in the Champions League standings with 11 points, having conceded only one goal.

With three games left, Ancelotti acknowledged it was a must- win clash in Bergamo but stressed that he was confident his players had what it takes to silence the doubters.

"(That is nothing more at stake) than three important points that will help us to qualify," the Italian told a press conference on Monday.

"Unfortunately we will have to play an extra round, but that's it, I have a lot of confidence in my team.

"Things have improved, we are now in a good dynamic and will keep improving as we move forward. Tomorrow's game could be the most difficult one between now and the end of the year.

"(My level of concern) is moderate right now ... moderate. We are worried about finding a good strategy to beat a very tough opponent like Atalanta. But nothing more ... moderate."

Ancelotti expects to face a much-changed Atalanta side from the one they beat 2-0 in the UEFA Super Cup in August. The Europa League champions are on a nine-game winning streak in all competitions, including wins over AC Milan, Napoli and Roma.

"Atalanta are doing very well, they have improved a lot compared to the Super Cup. They're on a roll and they're full of enthusiasm but that give us a chance to go out there and prove a point while earning three important points," Ancelotti said.

"They are a great team, a club that does a spectacular job despite losing a lot of players every summer. They always find ways to adapt and that says a lot about who they are.

"(Manager Gian Piero Gasperini) is doing a fantastic job. They change a lot of players every season, but he knows how to adapt always playing an intense, beautiful style of football. His work is spectacular."