Arsenal have completed the signing of Iceland international Runar Alex Runarsson, the club announced on Monday.
With Martinez gone, Arsenal were in the market for a backup goalkeeper, with Runarsson making the move to London to fill that role in a deal worth just over £1 million (€1.1m/$1.3m).
“We’re very pleased to welcome Alex to our squad,” said Arsenal technical director Edu. “We have been monitoring him for some time and from the analysis, he has strong attributes that we look for in a goalkeeper and as a person.”
Manager Mikel Arteta added: “We want to create healthy competition for places and we look forward to seeing Alex bring further depth to the goalkeeping position.”
Runarsson makes the move to Arsenal after two seasons with Dijon, where he made 13 appearances for the French side in all competitions last season.
He previously featured for KR Reykjavik in his native Iceland as well as Nordsjaelland in Denmark.
Internationally, the 25-year-old goalkeeper has earned five caps for Iceland and was a member of his country's squad for the 2018 World Cup in Russia.
He spent the weekend training with the Gunners and should be available for Arsenal's upcoming Carabao Cup clash with Leicester on Wednesday.
Leno has started both of Arsenal's Premier League matches this season, with the Gunners collecting a maximum six points from those two matches.
Goalkeeper Matt Macey had been named on the bench in each of those matches, with last season's backup Martinez heading to Villa after standing out in Leno's absence towards the end of last season.
It was Martinez that was in goal when the Gunners won the FA Cup, which proved to be an emotional send-off for the Argentine, who had been with the club since 2012.
Next up for Arsenal is a Carabao Cup clash with Leicester before a visit to Premier League champions Liverpool next Monday.