William Gallas says Arsenal will lose key competition at left-back if Kieran Tierney is allowed to join Newcastle United in the summer.
Tierney has been heavily linked with a move to St James' Park after falling behind Oleksandr Zinchenko in the pecking order under Mikel Arteta.
The Scotland international has not started a Premier League game since the turn of the year, and Newcastle are reportedly plotting a move in the region of £30 million.