The 22-year-old has attracted interest from Chelsea, Inter Milan, Barcelona and both Manchester clubs, with the Spanish outfit regarded as the favourite.
However, his future is unlikely to be decided until he completes his Copa America campaign for Chile.
“[Napoli have] made an interesting financial offer for Sanchez,” said Udinese owner Giampaolo Pozzo. “The deal would be complicated.
“We will have to wait until the Copa America is over and then consider how many pretenders there are and how many clubs are really interested in Sanchez. We need to understand who the real suitors of this champion player are.”
Contracted until 2014, Sanchez is valued at €50m (£45m).