"unlikely option" is a perfectly correct and usable phrase in written English.
You can use it when describing something that is not a likely or probable choice. For example, "Out of all the possible solutions, selling the house seems to be the most unlikely option."
Coach Randy Wittman sensed Gortat's difficulty and went to an unlikely option in the first quarter.
Any last-minute settlement is an unlikely option at this point.
No surprise, then, that default has suddenly become a – previously unlikely – option.
The feasibility of a large-scale conversion to irrigated coffee production is an unlikely option for these countries.
A third but unlikely option would be for the court to say it is powerless to decide the issue.
In both these series the heroine's Mr. Wrong does not vanish; he is pushed to the margins as a renewable, if unlikely option.
Instead, it protected the Jets-Eagles game, but that choice was made much earlier in the season before Tebow had become an unlikely option-running phenomenon.
They don't even merit analysis in the government's own research, which instead reckons unlikely options such as "influencing driving style" and cutting some motorway speed limits are better bets.
In my original article I did suggest that one of the other, if unlikely, options was that a second referendum could reverse the decision to leave the EU.
But, again, let's put aside these incredibly unlikely options for the likeliest.
They might be living in an underground base on Mars or the moon, or they could be residing in the asteroid belt (or any number of other plausible, albeit unlikely, options)." Considering these scenarios, what would we do if we encountered an alien race?
