Summer signing Maynard is likely to miss the rest of this season after tearing knee ligaments.
Mackay thinks that the 21-year-old can help make up the goal deficit and keep Cardiff in the promotion race come May.
He told Wales Online: "Joe has huge potential, he's a smashing lad and we have high hopes for him.
"He was a surprise to many people when he first came to Cardiff in terms of how quickly he learned and progressed. He came on leaps and bounds.
"He will be involved heavily this season."
Mason scored 12 goals last season for Cardiff and opened the scoring in the Carling Cup final against Liverpool, but has yet to start a Championship match for the Welsh side this campaign.