Manchester United will be in the market for centre backs this summer and another left-footer is actually becoming an increasing priority. United fans have wanted a new centre back for a while, but had focused the attention on another right-footer. The idea was to find the long-term partner for Lisandro Martinez in the heart of defence with Harry Maguire, Victor Lindelof, Raphael Varane and Jonny Evans hardly fitting that bill. However, Martinez has picked up repeated injuries this season and has only managed seven Premier League starts this term. United don’t have a like-for-like replacement a…