By Tobias Carroll Last summer, Cristiano Ronaldo left Juventus for a surprise return to Manchester United, the team he played for from 2003 to 2009. That was the point in his career when he first made his mark on global soccer, and expectations for what he might do there were high. Unfortunately, Ronaldo’s return to Manchester did not coincide with a successful season for his club team. Instead, Manchester United finished sixth overall, just above West Ham and a full 11 points behind fifth-place Arsenal. All of which might help explain why Ronaldo is rumored to be on the move again this summer…