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.
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