Highly unlikely = крайне маловероятно

Highly unlikely = крайне маловероятно

Красивое словосочетание, и очень легкое в использовании, поскольку оно сильно перекликается с русским языком.

 Как его использовать, ясно из примеров:

It's highly unlikely that the project will be finished on time.

However, such an outcome seems highly unlikely in the present political climate.

Personally I thought this highly unlikely.

Longman Dictionary of Contemporary English, Example bank

Highly unlikely of course there was even a shadow of truth in the stones and, even supposing, he thought a return highly inadvisable, all things considered.
 Ulysses, by James Joyce