Arsenal have approached Celtic with an improved bid in the region of £25m for Scotland defender Kieran Tierney.
The Scottish champions rejected an initial offer of £15m from the English club last month.
If the deal goes through, Tierney, 22, would become the most expensive player in Scottish football history.
The left-back, also linked with Napoli, is recovering from a double hernia operation after being restricted to nine appearances in 2019.
A £25m move would top the £19.7m Celtic received when Moussa Dembele joined Lyon in summer 2018.
Tierney has won four league titles, two Scottish Cups and two League Cups after coming through the Celtic youth system.