Jude Law will sport nothing but a napkin when he returns to television screens as the Young Pope later this year.

The British actor who plays the fictional first US pope in the hit series told reporters at the Venice film festival that it was "the smallest costume I was ever given."

A sneak preview of the follow-up series to the cheeky Vatican-set story called The New Pope screened in Venice Monday has Law's hunky pontiff fall into a coma.

He is replaced by the far more austere English pope, John Paul III, played by fellow Hollywood star John Malkovich.

But Law's Lenny Belardo (aka Pope Pius XIII) eventually comes to, leaving the world's Catholics with two competing leaders.

Trailers for the series, the brainchild of the Italian director Paolo Sorrentino, already have Law's risen again pope promenading on Venice's Lido beach in nothing but a pair of skimpy white trunks.

Sorrentino said he made Law suffer by forcing him to sport them on a nippy April day.

"You'll be surprised to know that those swimming trunks actually weren't the smallest costume I got to wear," Law teased reporters.

"There is actually a scene where I was wearing a napkin. It was truly the smallest costume I was ever given."