Leno cost Arsenal around £20million.
It was reported last month by BBC Sport's David Ornstein the Gunners were set to land Sokratis in a £16 million transfer.
Adli, who is an worldwide with France at youth level, was set to become one of new Gunners coach Unai Emery's first signings at the Emirates Stadium and even travelled to London with his agent Moussa Sissoko last weekend. The 29-year-old has just one year remaining on his contract with Borussia Dortmund.
Arsenal are looking to be busy in the transfer market as they look to build a squad capable of breaking back into the Champions League places under Arsene Wenger's successor Unai Emery.More news: Unleash Your Inner Jedi With The Classic Star Wars Gamer Bundle
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Leno is an interesting option for Arsenal, as he's one of the most gifted goalkeepers in German football, albeit not one of the most consistent.
German worldwide Leno began his career with Stuttgart in 2009 before moving on to Leverkusen in 2011.
Arsenal supporters will be hoping that some shrewd coaching can bring the best out of these two new acquisitions.
Arsenal were tracking Adli as early as March, when a source close to PSG revealed that Manchester City, Barcelona and Bayern Munich were also keen, but he was expected to sign professional terms in Paris until Emery's departure was confirmed.
The Gunners have not won the Premier League since 2004.