Arsenal will have to splash £25million if they decide to sign top target Chris Smalling from Manchester United. The Gunners are in the market to bolster their back line this summer with Per Mertesacker set to hang up his boots, according to the news . Arsene Wenger had been keen on bringing in West Brom defender Jonny Evans, who could only cost £3m this summer if the Baggies go down, but have turned their attention to Smalling. The England ace has come under fire in recent weeks for his duff partnership with Phil Jones, but has still played 30 times so far this campaign.