Should be fine, as long as you don't have any really big fish in there (not the Danios) to eat the small one.
BUT that said, occasionally fish will pick on a smaller fish, and sometimes the newbie will sort of be by itself. If you notice anything like that happening you can net up the others which are causing the trouble, let the newbie swim around for awhile and then add all the old ones back into the tank.
If still problems, you can redecorate the tank and move things around.
That gives all the fish a new place to check out and the territory from the established fish is changed/gone so they all kinda start fresh.
Occasionally it will just take a few days for the new one to become part of the team, you have a pretty small team, and so maybe no problems. The Danios like to have a bunch of buddies to hang with. They will tend to do better too.
