The Hoops were beaten 3-0 at Parkhead despite giving a hugely credible performance in the first leg of their last-16 tie on Tuesday night.
They were taught a harsh lesson by the Serie A champions, who opened the scoring after just three minutes when Alessandro Matri slotted home.
Celtic pushed for an equaliser and dominated for large periods of the game but were unable to make the most of their chances.
Claudio Marchisio added a second for Juventus on 77 minutes before Mirko Vucinic scored a third six minutes later to give them a seemingly insurmountable lead going into the return leg.
Lennon acknowledged that it will be difficult for Celtic to turn the tie around.
"We need a miracle," he said. "But it's the harsh reality of Champions League football and some of my young players will learn a huge lesson tonight.
"I thought for 70-odd minutes, until the second goal, we were by far the better side - but you can't give away goals like we gave away, sloppy.
"Efe was poor for the first goal but we had good chances to equalise. Then we switched off defensively for the second goal and the third goal was poor."
Lennon also raised concerns over the way Juventus - and Stephane Lichtsteiner in particular - defended corners, after the Swiss player was booked after tangling with Gary Hooper but continued grappling with the striker and also Ambrose and Scott Brown.
He continued: "I'd like to ask the referee, is the game different in Spain or Italy?
"Every time one of my players tried to move he was held. He should have given a penalty on at least two occasions."