The Englishman joined the French outfit on a five-month contract on a free transfer on transfer deadline day.
"Everyone talks about [Beckham's] image, but I want to emphasise his professionalism and quality on the pitch," Ancelotti told the club's official website.
"It is true that he is not young, but he has experience. [Paolo] Maldini won the Champions League at the age of 39, so Beckham still has lots of time ahead of him.
"He can play every position in midfield - defensive, with his passing ability, or on the right even if he does not have the speed of Lucas. He can help the team have a great season."
Beckham left MLS side Los Angeles Galaxy side in December.