Prime Minister John Key says National has yet to decide whether it will contest the East Coast Bays electorate in September's election.
There is conjecture National may do a deal with the Conservative Party and not run its current MP, Murray McCully, in the seat in a bid to bolster any post-election coalition.
New Zealand First leader Winston Peters has suggested he might also run in the seat, if a deal is struck.
Mr Key said a decision on the seat was close, but more likely next week than this week.
He said he would find such a deal very challenging, given National has always contested seats such as Epsom, where the winning candidate has subsequently become part of a government coalition.
