The 3-1 reverse saw Roma lose their round 16 tie 4-3 on aggregate.
Hummels was sent off on 11 minutes and Ranieri said afterwards: “Yes, it was a clear and obvious red card.
"He wasted time; he should have passed the ball to the left, but he didn’t. It happens, he’s a great champion, but it happens. Despite that, I want to congratulate the team, as the lads remained united in difficult moments and fought to the maximum.
“It’s a shame because we were feeling good and were convinced we could have a great match. These kinds of moments can go one way or the other, but I can’t blame the boys for anything. They played a fantastic game in a very difficult situation.
“We are still up there with the top teams, and we will do everything we can to take Roma as high as possible. I said it at the beginning of my journey in November, and I keep repeating it: I never give up. I always want the best, I demand it from myself, and I ask the same from the players.
“Give me a strong performance like today and we’ll have no regrets. We gave our all in an incredible and intense atmosphere, just like in the first leg at our stadium. Congratulations to them, but also to my players, who put in a great performance.”
Ranieri also explained the note he passed onto Athletic coach Ernesto Valverde at the final whistle.
He smiled: “We’re such good friends that I had actually lost his phone number! I told him, ‘Take this, I need to talk to you,’ because he knows a lot of Spanish players who could be of interest to me. That’s why I did it in front of everyone!"