World number one Novak Djokovic required medical attention after being struck in the head by a water bottle following his second-round win against France's Corentin Moutet at the Italian Open in Rome.

Djokovic was signing autographs after his comfortable 6-3, 6-1 victory against lucky loser Moutet when he was hit in the head by the bottle.

He immediately clutched his head and fell to his knees.

A spectator was leaning over the railing to hand Djokovic a notebook for a signature and the aluminum-type bottle fell out of his backpack.

Djokovic remained crouched on the ground for several seconds as staff ran to his aid and he was eventually helped off court.

Tournament organisers said there was no cause for concern over his condition.

"Novak Djokovic on leaving the Central Court at the end of his match was hit on the head by a water bottle while signing autographs [for] spectators," a statement read.

"He underwent appropriate medication and has already left the Foro Italico to return to his hotel."

Italian Tennis Federation spokesman Alessandro Catapano said Djokovic experienced some bleeding on his head but did not require stitches.

"Nole (Djokovic) was taken to his hotel and he seems OK. He was upset, but he seems OK," Catapano said.

"We're very upset about what happened and we are trying to figure out who it was and understand the dynamics.

"The police came and asked for information but the person who did it had already left."

Catapano added. "We're going through all of the video and camera angles to see if we can determine what exactly happened."

Djokovic was playing his first match since he lost to Casper Ruud in the Monte Carlo Masters semifinals on April 13.

He has a day off before his next scheduled match at the clay-court tournament.

The 36-year-old Serb is preparing to defend his title at the French Open, which starts May 26.

Meanwhile, Australians Jordan Thompson and Aleksandar Vukic both went down in comprehensive straight-set defeats in the second round.

Alexander Zverev crushed Vukic 6-0, 6-4 and Thompson fell 6-1, 6-3 to Brazilian qualifier Thiago Monteiro.

World number 11 Alex de Minaur is the only Australian left in the men's draw.

De Minaur plays Spanish clay-court specialist Roberto Carballés Baena in the second round in what will be his opening match in Rome.

Wires