O'Neill delighted with Johnson's winning Sunderland debut
It was he who set up both goals for James McClean as the Black Cats strolled to a 2-0 win to book their place in the draw for the next round.
O'Neill said: "Tonight it didn't seem to be a problem for him. In our side, he probably will have to do a little bit of that - James McClean does it almost automatically.
"Sometimes to forward-thinking players, you have to give that part of the game some consideration and during the course of the season, of course he will probably have to tuck in.
"But I think he can do it and I think he has got a willingness to want to do it. But mainly for us, he wants to get on the ball and that's something we want.
"The further that we have him up the field, probably the better for us. If he is picking it up, as he does, wide right-hand side with 40 yards to go rather than 70 yards, then it's better for us, so we will try to encourage that.
"But that said, during the course of the season, he will know himself, he will tuck in and defensively, he can improve - and I thought he did it fine tonight, really fine, just got back into position.
"Fine, he might not be the best in the world at doing it, but that's not the job that I brought him in to do.
"I want him to go and attack players like he did tonight and get the crowd on their feet, which he is capable of doing."