"It was a hard-fought game and in the first half the team held out well, but we conceded that Ibarbo goal right before the break," said Allegri.
"In the second half we started playing again and after the penalty had chances to win it. Unfortunately we were out of time and weren't sharp enough.
"We come away from Sardinia with a deserved point against a good Cagliari side."
Milan now sit in fourth place in Serie A, just three points behind Lazio in third.