SCOTTISH soccer champions Celtic have insisted they will not pay an outstanding GBP2.1 million demanded by Croatia Zagreb for the transfer of striker Mark Viduka. The Glasgow club have handed evidence to world soccer's governing body, FIFA, outlining why they refuse to honour the Australian international's initial contract. Viduka disappeared for five weeks after joining Celtic for GBP3 million two months ago. He has yet to play for them. FIFA had set a deadline of midnight on Friday for settling the bill, following Celtic's decision to pay only GBP900,000 to the Croatian champions. A Celtic spokesman said: 'We are sending a submission, as requested, and the matter is now in the hands of FIFA, which we feel is in everyone's best interests. 'We will be offering them [FIFA] a full disclosure and our co-operation with the aim of resolving matters to the satisfaction of all.' Viduka claims he had an agreement with Croatia Zagreb for half the fee of GBP1.5 million, while his old Australian club, Melbourne Knights, say they are due GBP600,000 as their share of the deal. It has been claimed in Scottish newspapers that Viduka's sudden departure to his Melbourne home on December 6 - citing 'depression' - came after he discovered Zagreb had told Celtic that the player was waiving his rights to any money from the transfer.