US Open champion Michael Campbell believes Michelle Wie has to prove herself on her own tour before she deserves to play against the men.

Wie could be one of the New Zealander's opponents when he defends his title at Winged Foot next month if she continues her progress through qualifying.

The 16-year-old Hawaiian has also been invited to play at the European Tour's European Masters at Crans-sur-Sierre in Switzerland in September.

Asked about Wie's participation at Crans-sur-Sierre, Campbell told reporters: "I can go two different ways on this question.

"I can be politically correct and say it's wonderful to see Michelle Wie at a European Tour event and to promote it.

"Or, I could say that she's got to prove herself that she can win on the women's tour before she can have a chance on the men's tour.

"Look at Annika Sorenstam, one of the best tournament golfers we've ever seen. She deserved to play on the men's tour in the US. Unfortunately she didn't make the cut.

"Michelle Wie is obviously a wonderful talent, but she needs to prove herself."

The teenager made her first cut in a men's event in the recent SK Telecom Open in South Korea.