The England international has been part of numerous campaigns for brands including Nike, Asda, Coca-Cola and Ford.
However, Stretford has admitted that it's difficult for Rooney to do required appearances for sponsors due to his commitments on the field.
Stretford told sportspromedia.com: "If I was looking after Rory McIlroy for instance and I tie up a deal in Korea and I want him to be in Korea on Wednesday to sign a contract and take a picture, within reason, provided Rory's happy, that's what would happen.
"But with Wayne you can't do that because you've got training, you've got games, you've got a very long season. At all times you can't lose sight of the fact of what it is that makes him the commercial clothes horse that he's become."
Rooney is currently in Portugal with his England teammates ahead of the World Cup in Brazil next month.