Tottenham coach Juande Ramos has warned his defenders he will bring in new blood this month unless they stop gifting goals to the opposition.Spurs have been vulnerable to set pieces in recent games and conceded two more goals in that fashion when beaten 2-1 by Aston Villa on Tuesday. A header by Olof Mellberg and a similar effort from Martin Laursen from a free-kick and corner respectively sealed victory for Villa either side of a Jermain Defoe effort. It means Spurs have now let in seven goals during their last three Premier League games. Ramos said: 'We need to find a solution to these defensive problems. If we can't sort the problems out with the players we already have here, then we will look outside for other players. 'We are lacking in some defensive departments and it is something we need to look at. We are paying dearly for those lapses. 'In the past few weeks we have made it a habit to concede goals from set pieces and it is hard to win matches when letting in so many goals in that way.' Ramos also insisted that Tottenham intend to try to hold on to star striker Dimitar Berbatov amid speculation linking him with Chelsea and Manchester United. His agent Emil Dantchev has already said the Bulgaria international would like to leave Tottenham if a club came in for him that matched his own ambitions. But Ramos said: 'Obviously Berbatov's agent is looking to do his business and has been making comments. 'But we are happy because we have the player on a contract and we plan to keep him.'