Rossoneri defender Kevin Constant was targeted by a home supporter in Sunday's Serie A match in a repeat of the incident involving Dani Alves at Villarreal
Just two weeks after Barcelona's Dani Alves had a banana thrown at him from the crowd in a Liga match at Villarreal, Rossoneri defender Kevin Constant was the victim in a similar incident in Bergamo, not long after conceding the penalty which allowed the home side to draw level.
Play stopped momentarily as the banana was cleared off the pitch to sarcastic applause from Nigel de Jong and Philippe Mexes, and Colantuono was disgusted that the incident soured his side's dramatic victory.
"I'm happy for the success, but the launch of a banana at Constant does not deserve recognition," he told reporters.
"It's a disgraceful act and I regret that one thoughtless fan could ruin brilliant day."
A brilliant late strike from Franco Brienza in injury time sealed the win for the hosts after German Denis had levelled in the second half following Gianpaolo Bellini's own-goal.
"I'm sorry that the people of Bergamo have only occasionally seen the true quality," Colantuono added of match-winner Brienza. "He has great quality and, as someone who coached him, I'm well aware of this."
Atalanta's triumph saw them reach the 50-point mark ahead of next weekend's final match of the season but they stay in 11th place, three points behind Lazio and six ahead of 12th-placed Sampdoria.
"It's certainly been a positive campaign, we've had a great season," Colantuono continued. "We believed in qualifying for the Europa League but we were punished for our physical exhaustion after six consecutive victories."
Milan, meanwhile, have seen their Europa League qualification hopes dashed following the defeat.