If it's not bleeding and wasn't bleeding, then you can clean it well and watch it.

If it were MY rat, I would in theory CONSIDER supergluing the cut, as long as it looked clean and I cleaned it thoroughly with betadine first. But if the cut is only 1/4 inch, that's pretty minor for a rat. I've had a couple that got cuts, I assume from a squabble, and once put into nice clean bedding cage for a couple days, it healed right up. I would have done more in treating it, but she was one of the very flighty rats and you couldn't really handle her without a full on fight.