Gunners captain Koscielny has told boss Unai Emery that he wants to leave the club and has received interest from several Ligue 1 clubs.
The Frenchman went on strike earlier in the week and refused to board a plane with the rest of the squad bound for America.
Portugal international Dias has been on Arsenal’s radar for a while and they considered a move for him at the start of the transfer window.
But it was decided that bringing him in would be too costly with Benfica likely to accept anything less than his £54m release clause.
Manchester United have also been linked with a move for Dias as they look for much-needed defensive cover.
The Gunners are rumoured to only have a transfer budget of around £45m to spend this summer after missing out on a spot in next season’s Champions League.
Spending all and more of that on a centre-half would not seem likely, meaning Emery would have to sell players to fund a deal.
Even before the Koscielny debacle the boss was on the hunt for a potential new centre-half, but other positions such as left-back and midfield are deemed to be the priority.
But, according to the Daily Mail, having scoured the market this summer they are set to turn back to Dias in their pursuit of central defensive reinforcements this summer.
The report suggests that Arsenal boss will attempt to to negotiate a deal with Benfica made up of a lower initial fee and future add-ons.
Dias has made almost 100 appearances for Benfica and won 11 Portugal caps since making his international debut last summer.
He was part of Portugal’s World Cup squad last year and helped his country win the Nations League in June, playing in both games against Switzerland and Holland.
The Gunners could end up being desperately short of central defenders should Koscielny and the unwanted Shkodran Mustafi move on.
That would leave Sokratis Papastathopoulos as the only other centre-half should they not sign any replacements.
Arsenal are also trying to sign Celtic left-back Kieran Tierney and Crystal Palace star Wilfried Zaha.
Initial offers for both have both been deemed way off the mark by both respective clubs, however.
With just four weeks left until the start of the new Premier League season, time is running out for Emery and Arsenal.