Aston Martin Formula 1 star Sebastian Vettel encountered an unexpected issue during practice for the Monaco Grand Prix.

The four-time world champion reported a vision problem during Free Practice 2 last night, telling his team over the radio that it “feels like my eye is bleeding”.

Vettel had been in the middle of a qualifying simulation run at the time, in preparation for his 13th start on the streets of Monte Carlo.

“I don’t know what was going on,” said Vettel.

“I had the first runs and something got into my eye, and then it got worse on the second run…

“It wasn’t bleeding, but I said [on the radio] either I’m emotional, or something else is going on because it was just tears and tears and I was blinking the whole lap. Not ideal on a track like this.”

Aston Martin humorously responded to the situation by gifting Vettel an eye patch to wear.

“I probably think I’ll keep that and it will keep me safe for the rest of the weekend,” Vettel laughed.

The 33-year-old, a two-time winner of the Monaco Grand Prix, showed solid form in Thursday practice, finishing inside the top 10 in both sessions.

“I was quite happy,” said Vettel.

“We got into a rhythm quickly, and then as I said, in the afternoon, lost a bit of [vision], but overall it’s okay.

“It will be tight, it’s always tight here and it’s obviously tight in the midfield and hopefully we can be at the forward end.

“Hopefully we can keep that up and get everything together,” he added.

“It’s all about Saturday afternoon, which is not tomorrow, the day after tomorrow, so a bit of time.

“We tried some bits, and like Monaco usually, you have a bit of stop and go, not getting the laps, that’s for everyone. It will matter on Saturday afternoon to get everything in that one lap.”

Practice 3 will get underway from 20:00 AEST on Saturday, before the all-important qualifying battle to set the grid for Sunday’s race.