The Scotland international is a major target for Arsenal this summer and the Premier League side have already had a £15 million bid rejected.
According to the Telegraph, Napoli will sell their current left-back Mario Rui this week to raise the funds needed to make an offer for the 22-year-old.
Celtic value the youngster at £25m, and while Arsenal had hoped to do a deal for less than £20m, Napoli’s heightened interest could raise the price tag if a bidding war breaks out.
Rui is believed to have been told he is not part of Carlo Ancelotti’s plans for next season in Naples, and has been linked with a return to his former club Benfica.
Tierney will be allowed to leave Celtic Park as long as the Scottish champions receive a bid that they deem to be acceptable.
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.