How large is it would you say? Even as big as the Scarlets are, they can't lose much blood without it being potentially dangerous. If it is small, apply a paste to the affected area, made from a mixture of water and flour. Or, buy KwikStop paste for it. Either way, it will dry up nicely. I prefer the flour-paste because it is cheaper, it doesn't sting, and for convenience. I had this happen before, did the above; all went well. Hope it works for you!
May I ask, where is the blood coming from? Is it a blood feather, or a scratch/scrape?