It marked a first goal in the Premier League for the Swede.
"It is important for Alex to get goals as a striker and it was a great goal," said Van Dijk.
"In terms of what I’ve seen of him, everyone knows and sees and experiences as team-mates how outstanding he is. It is about getting games, confidence but obviously scoring goals as a striker – that’s the main trigger for him.
"I’m not worried at all about him whatsoever. We want more than goals from him and that’s what he can bring and he just has to keep going and keep working, keep staying fit and keep staying important for the football club because I think he will and he already is."
Van Dijk added: "It is quite an understatement to say he’s had a tough year. He can probably explain it better but the injuries he had and the timing have been bad.
"But now he is fit and we all know what he can bring and he shows it in training and in games as well. It is on him now to keep showing that – hopefully after the World Cup because at the World Cup we (Van Dijk's Holland and Isak's Sweden) play against each other so he can take it a little bit easier then!
"We are happy and I am pleased with him and the work he puts in and am fully confident it will be absolutely fine for him."