<text>  Arsenal have put a new central defender on their summer shopping list, throwing Per Mertesackers role at the club into doubt. Gunners scouts have been instructed to identify potential central defensive targets this summer, despite the fact Gabriel only arrived from Villarreal in January. Borussia Dortmunds Neven Subotic has been scouted in recent months, while Aleksandar Dragovic is also on the clubs radar. Per Mertesacker impressed in Arsenals victory at Manchester United in the FA Cup on Monday evening . The World Cup winner, pictured celebrating with Aaron Ramsey, has been criticised this season . Gabriel and Laurent Koscielnys place in Arsene Wengers plans for next season look secure. But the arrival of a new centre back in the summer is likely to have repercussions for Mertesacker. The Germans performance have been criticised this season, though he was excellent in Mondays euphoric FA Cup win over Manchester United. Borussia Dortmund defender Neven Subotic has been scouted in recent months by Arsenal . Aleksandar Dragovic, pictured in action for Dynamo Kiev, has also been targeted by the Gunners . He was recently dropped by Wenger, but Gabriels hamstring injury has seen the defender handed an instant route back into the first-team. And the arrival of a new centre-half could marginalise Mertesackers role in Wengers plans. The capture of a new central defender could also have consequences for Calum Chambers. The England international has been used as cover at centre-back this season, but the clubs transfer plans could mean Wenger sees his long-term future at right-back or holding midfield. 