Klopp said: "Super intense. United had a really good start in the game, we didn't. We used the time and adapted well. We were outstanding but we had to finish the game off and we didn't. If you're only one goal up it's clear you're opponent is there. We lose it in the end. I cannot ask for me.
"The boys gave everything. Our decision making was not great. You have to accept the result. They deserve to go to the next round. It was a period in the second half when we should have finished it but we didn't and we know they could come back.
"I think my boys showed incredible character again. Super effort again. Everybody showed it. You cannot compare our season to United's with the amount of games. It's fine, we deal with it.
Now, the boys go on international duty. We hope they come back healthy. Lucho (Luis Diaz) felt his groin, Darwin (Nunez) hamstring. Cody (Gakpo) twisted his ankle. They play again in four or five days, it's crazy. Hopefully we will finish the season in style.
"I really feel for our people. In a few weeks we come again and we give it another try.
"How could I doubt the character of my boys? I don't. We use the situation and it's game over. We didn't use it and they ran through. I'm still proud of what I saw today. They boys have to recover and we will go for everything after the international break."