Arsenal have defensive problems ahead of Boxing Day in EPL.Unai Emery’s side hasn’t lost in their last 14 EPL matches, however Gunners coach may face problems in future as Rob Holding will be out for several months, while Laurent Koscielny is yet to come back after the injury he suffered last season. With only Sokratis and Mustafi in the center, Emery might consider a move for another center back, as he prefers to play with 3-4-3 in recent matches.Here are 4 options provided by Evening Standard.Eric BaillyCurrent club: Manchester United:Current market value: €30 mWhy he can leave Manchester United?Ivory Coast international has poor relationship with Jose Mourinho. Bailly isn’t playing much this season despite being included in starting lineup in the past matches. Gary CahillCurrent club: ChelseaCurrent market value: €10 mWhy he can leave Chelsea?Cahill doesn’t play under Maurizio Sarri. He can be a short-term replacement for Rob Holding until Arsenal will go for a center back in summer of 2019.Fernando CaleroCurrent club: ValladolidCurrent market value: €5 mWhy can leave Valladolid? Arsenal scouts have been watching Calero recently. 23-year-old defender has 10 m release clause in his contract, while his market value is two times less. Arsenal can buy him simply by paying the release clause. Calero is a cheap option, however, he has already impressed with his performances in La Liga. Chris MephamCurrent club: Brentford FCCurrent market value: €8 mWhy he can leave Brentford? Mepham, like Calero, has impressed with his performances. He is also a cheap option and Arsenal can be an attractive choice for 21-year-old player, who can jump from Championship to Premier League top-6 and Europa League.