The sale of Novartis AG's biosimilar copy of Amgen Inc.'s Enbrel will be delayed to 2018 due to a patent protection challenge in U.S. federal court, Reuters reported Jan. 25.

The U.S. FDA has already approved the biosimilar copy of Enbrel, called Erelzi, for rheumatoid arthritis, plaque psoriasis, ankylosing spondylitis and other diseases. But Amgen claims that the drug has patent protection until 2029.

Richard Francis, head of Novartis' Sandoz generics business, reportedly stated that the legal battle could take at least a year.