Remo Freuler was sent off with a straight red card just 17 minutes in, judging Ferland Mendy's run to be a clear scoring opportunity when he had knocked it sideways and seemed to be going for the cross.
La Dea held out brilliantly for most of the match, capitulating only to a Mendy curler at the 86th minute.
“What remains is the bitterness that we couldn't get to play the game we were waiting for," Gasperini told Sky Sport Italia.
“Aside from the result, the satisfaction was getting to play against Real Madrid in the Champions League. I don't know what the result would've been, but the game was completely ruined by an incident that was judged excessively.
“Qualification puts us in a way in the best possible position, as we only have to win and can't think of anything else! We had hoped for a different result, and above all a different match.
“We were in the final minutes, we just had to bring the result home. Yet we conceded a goal with Mendy's right foot, so that's a bit weird, almost a fluke. It's a pity.
“Considering how the game went, a 1-0 result isn't even that bad, but we feel regret that we weren't given the opportunity to play."