"Kate fancied a little pampering when she went to New York for the launch of her clothing range in Topshop," the Sun quoted a source as saying.
"She normally uses beauty salons in the five-star hotels she stays in but she decided to pop into a parlour in New York. She regrets the decision now as the nail on her big toe on her right foot has turned yellow and has become really thick and ugly. She is certain she caught a fungal infection from the cheap salon," the source added.
The 35-year-old had been allegedly looking forward to spending the weekend with beau Jamie Hince at the Coachella Festival in California. The source added: "Kate was looking forward to letting her hair down with Jamie at the festival. But she knows she"s going to have to lay off the booze for the duration due to her medication."