Van Dijk is in contention for player of the year awards in England thanks to his transformative effect on Liverpool since becoming the world's most expensive defender when moving from Southampton for £75 million ($98 million) last January.
However, the Dutchman believes a collective effort is required to halt Messi, who has scored 45 goals this season, two of which helped Barca beat Manchester United 4-0 on aggregate to progress to the last four.
"I think he's the best player in the world but we'll see. It's going to be a great match-up for all of us," said Van Dijk, who netted himself as Liverpool thrashed Porto 4-1 on Wednesday to complete a 6-1 aggregate victory.
"It's about doing it all together, it's never one-v-one, it's never just me against a particular striker.
"It's always us against everyone and I think that's the only way we can defend well."
Liverpool's defence could be further bolstered for the Premier League and Champions League run-in by the return of Joe Gomez.
Gomez formed a formidable partnership with Van Dijk earlier in the season before breaking a leg in December.
Gomez made his return as a substitute in northern Portugal and is also preparing himself for the prospect of facing the "best player in the world" in Messi.
"It'll be a difficult game. They're one of the best in the world, clearly, and they've probably got the best player in the world and many others around him," said Gomez.
"So it's going to be a difficult game, but that's what the Champions League is about.
"You don't get this far to have easy games and we know you have to earn your place in the next round."