Campbell has found first-team opportunities at the Stadium of Light limited this season and is out of contract in the summer.
The 25-year-old had been tipped to rejoin Hull, where he previously spent time on loan from boyhood club Manchester United, but could now be set for south Wales.
"We are interested in the player," Mackay told reporters.
"We are in discussion with Sunderland. They have put a price on the player and it is something we have to discuss with the club."
Any Cardiff switch for Campbell looks likely to depend on the outcome of Sunderland's reported attempts to sign Danny Graham from Swansea.
Campbell joined Sunderland in 2009 after departing Old Trafford, where he came through the youth ranks.