It is least probable that many....
It is less probable that many...

Thanks

Both are correct. They have different meanings though.

Thanks for the response : ) I know that both are correct, but I was wondering which one to use for the portion of the sentence that I gave. Is the remainder of the sentence needed? Thanks again.

It is not possible to determine which is correct from the portion you gave. I suspect this would need quite a bit of context to determine which to use.

less < less than other options
least < the lowest of all options