Rehab singer Amy Winehouse's appearance at the famed Grammy Awards has been thrown into doubt because she has allegedly failed to give up drugs and partying. The star was rumored to be making her musical comeback at the star studded ceremony next month, after taking a month of to recuperate following the cancellation of her U.K. tour last month and the jailing of her husband Blake Fielder-Civil. But reports claim Winehouse will face drug testing prior to being issued a visa to enter the country, something that would require the singer to have been free of drugs for a number of weeks. A source tells Britain's The Sun, "Amy's been told she needs to pass a drug test before she can get a visa. "She is doing much better and has cut down her drug use but is still isn't clean. Her recent holiday in Mustique was about cleaning up and it did help. But it is hard to believe there will be a time before going to the United States that she could pass the test. Her team are desperate to clean her up as the Grammys is such a big deal. But Amy's not so bothered." Winehouse has been nominated in six categories at this year's awards, including Album of the Year and Best New Artist. The ceremony is set to take place on February 10.