Safety fears may force singer Madonna to change the location of an upcoming Moscow concert, according to reports.
Madonna is scheduled to perform in Denmark on Thursday
The star is scheduled to make her first appearance in the Russian capital on 11 September as part of her world tour.
But authorities are considering moving the gig from near Lomonosov University to the city's Tushino airfield.
There are fears students could fall out of windows in their attempts to watch the concert, said Mr Nikolai Koulikov, head of Moscow's security department.
"The question of where the Madonna concert will eventually take place has still not been resolved," he told the Agence France Presse news agency.
The Luzhniki stadium, Russia's biggest sports stadium, will be unavailable as it is hosting a football match.
However, Mr Koulikov said there were no plans to cancel the concert despite a bomb attack on a Moscow market on Monday that claimed 10 lives.
"Life must go on despite these explosions," he said.
Madonna performed in Hamburg on Wednesday as part of the German leg of her Confessions tour.
The German concerts went ahead despite threats of legal action over the US singer's staging of a mock crucifixion during the show.