The manager has concerns over his group of five central defenders withstanding the demands of a long campaign In Leny Yoro, Ayden Heaven, Harry Maguire, Matthijs De Ligt, and Lisandro Martínez, Michael Carrick can talk of high potential: seasoned operators who will patrol the Manchester United backline safely. Except the 44-year-old privately harbours concerns about the five central defenders, especially as there is no plan to strengthen in the position unless one or more departs. Are they an i…