Blazevic included Medunjanin in his squad for the ties on November 14 in Lisbon and Zenica four days later but the Real Valladolid midfielder must first get clearance after playing for the Dutch U21 squad.
"The procedure for changing his soccer nationality is in progress and we expect a positive reply from FIFA by the end of the week," Blazevic told a news conference on Wednesday.
"We've asked for a summary procedure because we are running out of time and we are all hoping that Medunjanin will be cleared to play for us," added Bosnia's FA secretary general Munib Usanovic.
Blazevic, who steered Croatia to the 1998 World Cup semi-finals, has opted to set up Bosnia's training base for the playoff against Portugal in Croatia's coastal resort of Novi Vinodolski due to its mild winter climate.
"The conditions in Sarajevo are no longer ideal because of bad weather and we have opted for Novi Vinodolski because its climate is very similar to Portugal's at this time of the year.
"I have never been involved in a more important match in my career, there is a lot of pressure and great expectations among the fans so we mustn't let them down," said Blazevic.
"We can't imagine that we will get through the first leg without any new bookings because the Portuguese force yellow cards from the opposition with their skill and ball control.
"We have a lot of players who are in a precarious position and that's why I have called up 26 players for the two games."
