The 20-year-old has returned to Brighton after scoring twice in seven appearances for the Dons before a foot problem halted his progress.
But Ardley remains hopeful that the winger will return to the club next season after impressing during his stay.
He told the Dons' official website: "We wanted to keep Brennan but it would have taken him two weeks to return to training and another week to get fit. That would effectively have been the season over for him.
"Maybe we will work with Brennan again next season. He was brilliant and I think the fans really took to him as well."