The Celtic boss describes both defeats - the only losses they have suffered in domestic football since last April - as bitter disappointments.
But Lennon contends there were some mitigating circumstances when they were at the wrong end of a shock exit from the League Cup in September at the hands of Morton.
The Hoops were still engaged in a Champions League group stage campaign at that time and fielded a weakened team against the side battling relegation to League One. Against Aberdeen, they went in all big guns blazing - only to see the Dons wrench the dream of back-to-back doubles from their hands.
So, when asked which of the two cup defeats was the tougher to take, Lennon responded instantly: "This one is far harder because we were more or less full strength on Saturday and we were going very, very well going into it.
"So, it's a sore one."
While the league championship has always been the main priority this season, Lennon is not prepared to dismiss the cups as unimportant.
Along with his backroom staff, he will carefully analyse how they managed to surrender an early lead, and fail to put any real pressure on Dons keeper Jamie Langfield in the 40 minutes after Peter Pawlett put Aberdeen ahead at Parkhead.
"We need to look at the mentality, look at the way the game went and why it went the way it did - and make sure it doesn't happen again," said Lennon.
"Sitting down with the players and going through the match again is not something I do normally, but maybe on this occasion I will."
Even before the post mortem at Lennoxtown gets under way, Lennon believes he knows the major flaws which exposed them to not only losing their clean sheet record, but also the match.
He said: "When your passing goes and there is a lack of communication, you get punished. And that's exactly what happened."
The manner in which the goals were conceded particularly irked Lennon, not least because his players had been well warned what to expect.
"We talked about set-pieces all week because we felt that would be Aberdeen's best chance to get into the game," he explained.
Lennon knows that, over the course of a season, there is always the possibility his side would have an off-day.
But, he insisted that, of all days, this should not have been the day.
It was a pivotal game for us," he said. "We didn't want to go out of the competition.
"We didn't work their keeper hard enough, and our decision-making and the quality of our play was poor."