Arsenal will sell Tierney if the price is right.

Noel Whelan believes Arsenal ready to let left-back Kieran Tierney leave the club for the remainder of the summer. After being link with Manchester City team of rivals in the Premier League.
Mikel Arteta tried to correct the problem at left-back last season. From the Scotland star striker suffered a serious injury with the signing of Nuno Tavarez, including pulling Oleksandr Zinchenko came from City in the summer and in the past two games the Ukrainian has impressed and became the Spaniard’s first choice.
At the same time, it is reported that Manchester City are also interested in bringing Tierney to the Etihad, and Whelan believes that if Arsenal receive a satisfactory offer they will. May be ready to let the Scottish left-back leave the team, even though he is an important player.
“I don’t think it would hurt anything if Arsenal wanted to sell him out. They were clear that Zinchenko was the first choice. That’s why he started in the starting XI. While Tierney was on the bench.”
If Arsenal get a satisfactory price from City. I think they have no reason to think too much. They can set whatever price they want. And it will a price that you probably won’t find in the next season.”