Manchester United have enjoyed a pretty successful summer to date, but Rene Meulensteen is yet to be impressed. So far this summer, four major arrivals have joined the ranks at Old Trafford, ticking off every weakness – bar one – that the squad had at the back end of last season. Manchester United have brought in two central defenders, along with a striker and a full-back. Only a midfielder is missing from making this a perfect summer for the Red Devils. Matthijs de Ligt and Noussair Mazraoui were both confirmed on Tuesday, but their arrivals have been controversial, to say the least. Paul Sch…