Van Dijk said: "Obviously it's not great. A very, very disappointing evening. Too many individual mistakes and we got punished for it. It feels bad.
"With the man-marking system they do, we have to do much better. When we have the ball we have to do better and be much stronger. The spaces were open and they punished us immediately.
"A very disappointing night for all of us but we can't dwell on it for too long. We need everyone to look forward to another big game. We have to switch back onto getting results.
"We were wide open. It's more that we conceded the goals because we lost the ball in difficult areas. It hurts. But it can't put us down. We have to react pretty quickly.
"It hurts of course. We haven't lost here for a long time. But we shouldn't take the credit away from them. They punished us for being sloppy in possession. We still had chances to score one or two and unfortunately we didn't.
"If you don't believe, there's no point going to Italy. We have made it very hard for ourselves going there 3-0 down. But the way to bounce back is by winning the game on the weekend. We need everyone to switch it back on. Then we can focus on putting out at least four goals over there."