Valencia's Shkodran Mustafi has agreed to join Arsenal but the clubs have yet to finalise a fee, according to Sky sources.
Arsene Wenger is in the market for a centre-half after Per Mertesacker suffered a long-term knee injury and Gabriel was ruled out for up to eight weeks.
Sky in Germany are reporting that Mustafi has agreed to move to the Gunners, although sources say the player has signed nothing and there is no agreement yet between the clubs.
The 24-year-old Germany international, who is valued at around £30m, is still training with Valencia, and Wenger's immediate focus is on preparing a team - including a makeshift defence - for Sunday's Premier League opener at home to Liverpool, live on Sky Sports.
Laurent Koscielny returned to training on Wednesday but has already been ruled out by his manager, who does have England U21 duo Calum Chambers and Rob Holding available.
Nacho Monreal and Mathieu Debuchy have both filled in at centre-half in the past and are more experienced options.
Mustafi, 24, was on Everton's books as a youngster and played for Sampdoria before joining Valencia in August 2014.