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, and played in two winning Scottish Cup finals and two triumphant League Cup finals after coming through the Celtic youth system.