Rival Donaldson to join Trimble team in peace talks.
Members of UUP executive were told at a meeting in Belfast that Mr Donaldson would take part in the negotiating team next week at Downing Street.
Sources said the Lagan Valley MP, who had been touted as a possible leadership challenger, will join UUP leader David Trimble and Stormont minister Michael McGimpsey at crucial peace process talks involving Tony Blair, Irish Premier Bertie Ahern, the nationalist SDLP and Sinn Fein.
The talks will aim to resolve differences over IRA disarmament, policing, the scaling down of Army bases and personnel and sanctions against Sinn Fein.
There had been indications from Mr Donaldson's supporters earlier in the day that the Lagan Valley MP had until Monday to decide whether to mount a leadership challenge to Mr Trimble at next week's meeting of the Ulster Unionist Council. It was not clear if the move to include him on the negotiating team would relax the pressure on Mr Donaldson from anti-Good Friday Agreement elements in the party to stand.
Mr Trimble's leadership of the UUP has been called in question since the party's losses in the Westminster and local government elections.
The UUP has lost four House of Commons seats since the 1997 General Election while their rivals in the Rev Ian Paisley's Democratic Unionists have gained three. Mr Trimble's leadership of the UUP will have to be ratified by the party's 860-member ruling council at next week's annual general meeting.
Veteran South Belfast MP the Rev Martin Smyth challenged the Northern Ireland First Minister at last year's annual general meeting and secured 43 per cent of the vote.
Mr Smyth, a former Orange Order leader, has signalled he is willing to run again.