Arteta clearly did not view Sead Kolasinac as reliable cover for Tierney, allowing the Bosnian to rejoin Schalke on loan earlier this month.
But Kolasinac must be replaced before Monday’s deadline.
Arteta recently hinted that he is looking at strengthening at left-back, so it is clear he is not completely satisfied with his options in that position.
“With the departure of Kola, we are a little bit short with left-footed full-backs at the moment,” Arteta said.
“We know we can use Ainsley there, we can use Bukayo there and we can use Cedric – who has played in that position – so we have some options.