Colton Underwood thinks Becca Kufrin's 'Bachelorette' runner-up has what it takes to slip into "The Bachelor" tux next -- but he also thinks he ain't that special.

We got the ex-NFL stud, and famed virgin, Tuesday in Venice and he said Blake has a really good shot, especially after the emotional breakup scene ... which he considers authentic, raw emotion.

Not sure if Colton's vote of confidence carries much weight though, because he says all the other fan faves from this season -- and even an Arie-like old-timer -- are right there in the mix too. Fact is, Colton's playing coy for his top pick -- even when it comes to himself.