Manchester United striker Joshua Zirkzee is on international duty with the Netherlands, taking a momentary breather from a frantic start at Old Trafford. After coming in cold with a lack of pre-season, Joshua Zirkzee went straight into the mix with a debut goal against Fulham. A couple of less successful games later, and Zirkzee is getting a rude wake-up call, learning that United have real challenges to overcome. Zirkzee has told the Dutch media he believes United will come good, citing what he believes are encouraging signs during training at Carrington. READ: Who is Joshua Zirkzee? Meet the…