He has not played for the Bluebirds since arriving on loan until the end of the season.
But there are still 12 games left in the season, and Harris hopes that Smith will be involved sooner or later.
Smith is 25 and is hoping to get game time so he can secure a permanent move in the summer.
"Brad has worked extremely hard to get up to speed," Harris said to reporters last week, before his side lost 2-0 to Stoke City.
"It's not just fitness-wise, it's building up an understanding of the way we play, combinations with wide players and centre halves around them, getting to know the group culturally.
"They (Smith and Dion Sanderson) have trained really well and they are really, really good lads. They have definitely improved us as a group.
"We really look forward to seeing them in a Cardiff City shirt."