The Ibrox side had a mountain to climb after conceding twice in the first 16 minutes but created chances before a third goal was given up ten minutes from the end. There were, however, "definitely" positives for the Dutchman.
"I think we gave the goals too easily. After that we reacted really well, stayed in the game and could have scored just before half-time,” he told BT Sport.
"Second half we showed character. I think we were well organised defensively and didn't give any big chances away and were creating a lot of chances. In the end you concede the third goal by a set piece.
He added: "You have to step up your level. We play against the leaders of Italy, they are flying, and I think we gave them a really good game. I think we created the most chances in a Champions League game this season."