However, Robertson believes that the 24-year-old will bounce back from his horror show, insisting that he has what it takes to become a "top, top keeper".
"We win as a team, we lose as a team. We fell short. Of course he made mistakes. He did. But we are not blaming him," Robertson told reporters.
"He will hold his hands up. He has been incredible since he go the number one jersey. He is young and he will learn from it. He will be a top, top keeper.
"We have fallen short and there are no words that we can say to Loz that will make it better for him. We went around him. We all gave him a hug and tried to lift him. I don't think anyone thought that was going to happen."
Karius kept more clean sheets than any other goalkeeper in the Champions League this season.