Per the source, the Gunners are considering making a late move for the Turkish international as talks with Valencia defender Mustafi drag on.
Arsenal boss Arsene Wenger is currently facing a defensive crisis with Per Mertesacker out injured until December and Gabriel could be sidelined for eight weeks.
To make matters worse Koscielny is unfit and missed the opening game of the season against Liverpool which the Gunners ended up losing 4-3 at the Emirates.
Toprak did recently hint that he could leave the Bundesliga outfit over the summer transfer window.
Toprak was quoted by Turkish-Football.com as saying: “It is not certain whether I will stay at Bayer Leverkusen, we still have a month and anything could happen until them.”
The 27-year-old has no shortage of suitors and the Daily Star did report back in March that Toprak was a top Manchester Untied target.
The Red Devils have been keeping tabs on Toprak who wanted to remain at Bayer at the start of the transfer window.
Toprak does however, want to play in the Premier League and Bayer may want to cash in considering he has just two-years remaining on his current contract.
The powerful defender has years of Bundesliga and Champions League experience as well as international experience.