Jamie Redknapp says Kobbie Mainoo is facing a much tougher challenge at Manchester United than Phil Foden ever has at Manchester City. It’s been a fantastic March for Kobbie Mainoo as he played a key role in the FA Cup triumph over Liverpool which earned him his first England call-up and debut. The 18-year-old earned rave reviews for his Player of the Match performance against Belgium for the Three Lions but came back to earth on Saturday night. While Mainoo himself wasn’t the worst offender, he was back in a United side that seemed to have lost all the spark and fight it showed against Liverp…