Plans for GB football teams to compete at London 2012 have been thrown into confusion by the Irish FA's revelation that it is against the plan.
Raymond Kennedy's comments are likely to surprise the BOA
British Olympic Association chief Simon Clegg told BBC Sport that men's and women's teams would be fielded in 2012.
He added that "Northern Ireland had been supportive".
However, Irish FA president Raymond Kennedy said on Monday evening:"The Scots and Welsh are very much against it and we'll be weighing in with them."
Kennedy added that the IFA "would not want to compromise our national identity".
"Someone somewhere down the line might suggest that maybe there should be an all-British team in world football," continued the Irish FA president.
"We have made our position clear that we are totally against a GB team taking part in the 2012 Olympics, either men or women.
"Sepp Blatter has said it would be a one-off but I would need further reassurance and maybe Scotland, Wales and Northern Ireland should get together and get further assurances."
On Monday, the BOA said it would press ahead with plans to enter British men's and women's football teams at the 2012 Olympic Games.
The International Olympic Committee (IOC) has written to the BOA confirming that the host qualifying rule will apply to all team sports in London.
"We will field a team," BOA chief Simon Clegg told BBC One's Inside Sport.
"And the comfort and commitment that we've now got from the IOC just reinforces that aspiration."
The BOA's confident stance comes despite vocal opposition from the Scottish (SFA) and Welsh (FAW) Football Associations - and latterly the IFA.
Clegg is likely to be surprised by Kennedy's comments on Monday evening.
The BOA chief spoke earlier on Monday of the IFA's support for the plan.
However, it now appears as though Northern Ireland support for the initiative has disappeared.
Under Jim Boyce's presidency, the Irish Football Association had been careful not to rule out Northern Ireland involvement in the Great Britain team but current IFA president Kennedy has made up his mind on the issue.
Speaking about the issue in December 2005, Boyce spoke of prospects of 2012 Olympic football matches being played at the mooted multi-sport stadium which is being proposed for Northern Ireland.