German prosecutors are to monitor Madonna's concert to determine whether a mock crucifixion could be construed as insulting religious beliefs.
The cross use has been criticised in most countries on the tour
The segment of her tour where she appears on a cross wearing a crown of thorns has provoked controversy in several countries.
Prosecutors admit they will rely on media reports of the concert rather than send their own observers.
Madonna will play in Dusseldorf on Sunday, following on from her UK dates.
Religious leaders have objected to the performance, which Madonna says is part of an appeal for Aids charities.
Vatican Cardinal Ersilio Tonino, who spoke with the approval of the Pope, called the concert "a blasphemous challenge to the faith" and a "profanation of the cross".
He also called for Madonna, who was raised as a Catholic, to be excommunicated.
Muslim and Jewish leaders in Rome also raised objections before the star's concert in the city on 6 August.
However, the performance went ahead, including the segment on the cross.
Madonna's New York-based spokeswoman, Liz Rosenberg, denied that the star's show was insulting.
"The context of Madonna's performance on the crucifix is not negative nor disrespectful toward the church," she said.