By Matthew Cooper Manchester United will have to act fast if they are to sign Serhou Guirassy for a cut-price fee. The forward has been heavily linked with a potential move to Old Trafford, given United’s struggles in front of goal so far this season. The Red Devils have scored just 22 Premier League goals, only the current bottom two Burnley and Sheffield United have managed less, while big money summer signing Rasmus Hojlund has not made much of an impact. United forked out £64million to sign him from Atalanta and the 20-year-old has scored just six goals in 24 games – only one of which has …