Frei has been ruled out of Euro 2008 after suffering a knee injury during his side's opening defeat by the Czech Republic.

But the 28-year-old will be fit again in six weeks and has told Celtic boss Gordon Strachan to make a move if he is interested.

"Apparently Celtic were in for me in 2004 and 2006," Frei said.

"Now they want me again in 2008.

"However, no-one has ever put an offer on the table. If they want me they can phone me. Otherwise, I don't want to talk about it."