He has put his name forward to succeed Carl Bildt as the international community's "High Representative" coordinating the civilian aspects of peace-building in Bosnia.
Not all of those on the selection board are likely to be Portillo enthusiasts. The British representative on the steering board, is Robin Cook, the Foreign Secretary.
Mr Portillo is understood to have "made himself available" after he was approached by Mr Bildt. Mr Bildt was apparently impressed with what he saw Mr Portillo while in office.
The High Representative is not a UN appointee, but has an ill-defined role in overseeing the reconstruction of Bosnia and reconciliation of the former warring factions. He or she has no formal authority over the Nato-led military force, S-For, but in practice works closely with it as well as with the UN and local parties.
Many regard the job as a poisoned chalice. "Some of the best candidates, the ones who have a knowledge of the region, know better than to accept this job," said one diplomat in Sarajevo, who did not wish to be named.
The top contender for the post is the Spanish ambassador to the UN Carlos Westendorp. Mohamed Sacirbey, the current Bosnian ambassador to the UN, spoke favourably of him.
The only other candidates are Mr Portillo and an Italian senator, Giacomo Migone. The new High Representative is expected to be named next week - and Mr Portillo is still in with a chance.
Some diplomats say putting up a little-known Spaniard without experience in Bosnia could damage efforts to reunify the country. "That is not the right message to be sending right now", said one western diplomat in Sarajevo.
In his last report to the UN Security Council, Mr Bildt warned that Serb and Croat leaders were undermining the peace treaty through "creeping secessionism".
The slow progress on returning to normal has led to a divergence of views between Britain and the US. The US is still determined that the peace implementation force should be out on schedule, by July 1998. But Mr Cook warned this week that if a robust military force does not remain, the fractured country could return to war.Reuse content