Cristiano Ronaldo was unable to mark his return to action with a goal as Manchester United ended their pre-season campaign with a 1-1 draw against Rayo Vallecano at Old Trafford.   Ronaldo's United future has been the subject of intense debate this summer.     The 37-year-old is keen to move away from the club to pursue his desire to compete in the Champions League.   And he was allowed to miss United's pre-season tour of Thailand and Australia for personal reasons.   Ronaldo made a point of applauding fans on both sides of the stadium as he led the