A botched Greenpeace stunt was "reckless and dangerous", football chiefs have claimed.
A 38-year-old German activist parachuted into the stadium before kick-off of the Germany-France Euro 2020 match last night.
Two football fans suffered head injuries in the bungled protest, but the protester was not hurt.
UEFA said that the incident "could have had very serious consequences for a huge number of people attending".
The environment campaigner from Germany's Baden-Wuerttemberg state was arrested and detained by police.
He is being investigated for "several offences", police have confirmed.
Munich police said that the "the aircraft was seized" and that the force has "no understanding whatsoever for such irresponsible actions".
"Investigations are now being conducted into several offences under the criminal code and the air traffic act, among others," police confirmed.
There is no update on the condition of the two injured spectators.
Greenpeace issued an apology, saying the aim had been for the activist to drop a latex ball with a protest message onto the pitch.
The organisation said: "Technical difficulties forced the pilot to land inside the stadium. We deeply regret that this put people in danger and caused injuries."
It has admitted that the stunt did not go to plan.
Greenpeace said on Twitter that the protest was aimed at urging Euro 2020 sponsor Volkswagen to stop selling diesel and petrol cars.
Bavarian prime minister Markus Söder told local radio that the authorities are taking the matter seriously. Mr Söder said: "This was not a trivial offence."
The fiasco was captured on camera shortly before kick-off.
The activist was seen flying over the stadium in Munich strapped to a yellow parachute microlight before apparently getting tangled in overhead camera wires.
He was thrown off course and narrowly avoided crashing into the stands before landing on the pitch among the players.
His parachute had "Kick out oil!" written on it.
