"If he does come and enters Germany, then he will naturally be told in all clarity that what he said is absolutely unacceptable, criminal and far removed from reality," the head of the German football association said on Sunday, referring to comments Mahmoud Ahmadinejad has made about the Holocaust.
But Theo Zwanziger said he was against banning him from the tournament starting on Friday because that would only "make him a martyr".
Ahmadinejad has been criticised by European countries for his inflammatory remarks about Israel and statements questioning the extent to which Jews suffered at the hands of Nazi Germany and its allies during World War II.
Angela Merkel, the German chancellor, and other leaders have criticised his remarks as unacceptable but refrained from banning him.
Denying the Holocaust is a crime in Germany, punishable by up to five years in prison.
Ahmadinejad (R) receives a
jersey bearing his name
The Iranian president has left open whether he will attend the World Cup. Iran plays Mexico in their first match on June 11 in Nuremberg.
"My decision depends on a lot of different things," Ahmadinejad told a German magazine last week. "Whether I have time, whether I want to and some other things."
An Iranian World Cup 2006 song is available free at http://www.hamvand.com/, a Persian arts and culture site