Manchester City cruised to victory against Luton Town in the FA Cup – but there was one negative when Jack Grealish went off in the first-half with another injury. City thrashed Luton 6-2 at Kenilworth Road, with Erling Haaland the star of the show scoring five goals. Kevin De Bruyne assisted four of those goals, and Mateo Kovacic also scored to round off a great night. But there was one sour note, and that was when Jack Grealish limped off for City in the first-half with an apparent groin injury. The same happened for the England international when City played Copenhagen a couple of weeks ago…