Arsenal have submitted a bid for Benfica left-back Alex Grimaldo, according to reports.
The Gunners were unable to call upon the services of the Scotland international during the business end of the 2022/23 campaign, as Tierney went down with a knee issue in April.
The former Celtic defender missed 16 matches in total last term as Arsenal narrowly missed out on a top-four finish and Champions League qualification.
Nuno Tavares and Granit Xhaka deputised at left-back but Mikel Arteta is now considering bringing in a back-up from elsewhere after Tierney's latest setback.
Selected in the starting XI for Arsenal's pre-season clash with Nurnberg, Tierney came off after just 30 minutes.
Arteta insisted after the match that the early substitution was planned, but that has not stopped him submitting an offer for Grimaldo.
According to the Daily Star Arsenal have offered £5.9m for the Spaniard, who has been at Benfica since the start of 2016.
Grimaldo is out of contract next summer and the Gunners are therefore hopeful of landing him on the cheap.
But given that the 26-year-old appeared in the majority of Benfica's Primeira Liga matches last time out, Arsenal will probably need to increase their bid.
It is likely that their opening offer was intended as the starting point for negotiations, but the bid shows that Arteta wants a more reliable deputy for Tierney.
Tavares had some bright attacking moments last season but he is suspect defensively, while Xhaka is not a natural left-back.
"He’s really good," Arteta said of Tierney after the friendly against Nurnberg, which ended in a 5-3 Arsenal win.
"He’s been training really good. Obviously, he’s been out for over three months now so we wanted to give him a proper warm-up, play the first half an hour and then get him out. So he was in good condition and there’s no issues there."
