According to both English and Italian sources, Arsenal management are still planning to try signing Greek international centre-back Kostas Manolas (25) from AS Roma, as an additional backup to Koscielny and Mustafi, together with Gabriel Paulista, since Per Mertesacker isn't recovering easiy from his long-term injury. Italian club, which the player is currently on a deal with until June 2019, aren't however available to let him leave, and they'd rather sign him on a new contract.
Source: transfermarketweb.com