Manchester United have seen Lisandro Martinez suffer an injury-hit campaign and that means another left-footed centre back may be needed. Martinez is a quality centre back when available and one of the better signings made in the Erik ten Hag era. The Argentinian has endured a frustrating season though, starting just seven Premier League games having suffered multiple injury setbacks. United just don’t have anybody quite like Martinez, even just from the perspective of another left-footed centre back. Luke Shaw has filled that role at times but he has suffered injury problems too, meaning Unit…