Novak Djokovic says he felt hampered by the after-effects of being hit on the head by a bottle as he fell to a shock Italian Open defeat by Alejandro Tabilo.

The world number one was accidentally struck by the water bottle as he signed autographs following his second-round win over Corentin Moutet on Friday.

He struggled to find any rhythm against Tabilo on Sunday, with the Chilean needing just 67 minutes to win the third-round match 6-2 6-3.

"That has really impacted me a lot. After that I got medical care, [and went] through half-an-hour [to] an hour of nausea, dizziness and blood," said Djokovic.

The Serb initially made light of the incident when he jokingly wore a bicycle helmet to training on Saturday, but says he will now have further scans.

"I managed to sleep OK, I had headaches. The next day, or yesterday, was pretty fine, so I thought it's OK. Maybe it is OK, maybe it's not," he added.

"The way I felt on the court today was just completely like a different player entered into my shoes.

"Just no rhythm, no tempo, no balance whatsoever on any shot. It's a bit concerning."

It was a first career victory over a top-10 ranked opponent for Tabilo, who is ranked 32nd in the world.

The 26-year-old was dominant throughout, breaking Djokovic's serve four times and not conceding a single break point.

"It's incredible. I came on court just looking around and soaking it all in, trying to process everything. I'm trying to wake up right now," said Tabilo.

"I was just trying to keep my nerves and keep swinging. Every time you feel like you are close to the end your arms get a little tighter.

"I was just trying not to think about it and take it point by point. It's crazy, I can't believe what's happened."