New York: Frenchman Gilles Simon apologised "10 times" for accidentally hitting a ballgirl in the eye as he warmed up for his US Open fourth round tie against Marin Cilic on Tuesday.

The young, brown-haired girl was left in tears after the serve hit her square in the face on the Louis Armstrong Court before she took refuge out of harm's way behind the umpire's chair.

Gilles Simon
Gilles Simon. Pic/ AFP

"It's dangerous when you have a tennis ball in your eye. I just wanted to be sure she was fine, because I had the feeling she just wanted to stay on the court, but it was just really hurting her," said Simon, who went on to lose in five sets to Cilic.

"I asked her 10 times, and 10 times I had the same answer. I hope she's fine."

Luckily for the ballgirl, Simon has one of the gentlest serves on tour -- at the US Open his fastest was timed at a relatively sedate 127mph (204.3kmh) compared to the fastest clocked at 147mph (236.5kmh) which was powered down by Australia's Sam Groth.