Vonlanthen is the youngest scorer at a European Championships

"It's questionable whether he will make it," coach Koebi Kuhn said on Tuesday.

"We will keep an eye on him over the next two to three days to see if things change, but we're already afraid it won't be enough for the World Cup."

Vonlanthen, 20, became the youngest scorer in the European Championships when his goal against France in 2004 saw him beat Wayne Rooney's record.

Rooney had set the record just four days previously, in England's 3-0 win over Switzerland.

Kuhn is likely to call on attacking midfielder Hakan Yakin who narrowly failed to make the squad.

Yakin returned from injury to put in some strong performances for Young Boys Bern near the end of the season - but if he is called up, the Swiss will have only three specialist strikers in their squad.