“Thousands of people before me have tried to answer this question,” Goretzka replied Tuesday in Lisbon when asked how to stop Messi.
“It is nice – after playing against (Juventus star Cristiano) Ronaldo a few times – to play the other formative player of the last decade.
“That can only be done collectively,” the 25-year-old central midfielder said of Messi, “because he is a gifted footballer”.
“I don’t know how, but we have to force our game on them.”
Messi scored his 31st goal this season on Saturday and is looking to lift the Champions League for the fifth time in his career with Barcelona.
Treble-chasing Bayern, however, have won all 13 games since the coronavirus lockdown restart.
They underlined their impressive form on Saturday when Robert Lewandowski, the Champions League’s top scorer, netted twice and created two more in the last 16, second-leg rout of Chelsea to seal a 7-1 thrashing on aggregate.
Bayern are chasing the treble having already won an eigth straight Bundesliga title and lifted the German Cup, but Goretzka says Barcelona present a true test.
“There is no easy way now. We are here in the sun in Portugal and are preparing for a knockout game in the Champions League,” he said.
“We’re really up for it. Knockout matches are great.”
While Barcelona are packed with stars alongside Messi, Goretzka says Bayern are far more than just Lewandowski’s goals.
“At the moment, we’re playing as a unit, in addition to the quality of the individual players.
“We have a clear plan in hand and our intensity without the ball can make the difference.”
But he admitted being wary of Arturo Vidal, Barca’s ex-Bayern midfielder.
“I got to know him for a few weeks and played against him many times. He has a first-class mentality with amazing fitness,” added Goretzka.
“I noticed that during fitness tests – which I took next to him – he can go beyond the pain threshold.”