Manchester United youngster Radek Vitek is backing Andre Onana to continue progressing at the Premier League giants while sharing the advice given to him by the Cameroon international. The £47 million signing from Inter Milan is certainly not the first goalkeeper to endure a difficult start to life at Old Trafford. Fabian Barthez, a World Cup winner with France, struggled in his debut season at times. Ditto the legendary duo of Peter Schmeichel and David de Gea. Gary Neville wasn’t lying when he claimed, on Sky Sports, that the goalkeeper position at Manchester United is perhaps the most high-…