A maximum of 43,000 spectators can watch the match at the Ramón Sánchez Pizjuán Stadium in Seville.
Uefa, the European Football Association, also distributed only 9,500 tickets to each team before the match.
But in the city there are hundreds of thousands of visiting fans.
And already at midnight, the night between Tuesday and Wednesday, came the first reports of chaos.
Five German supporters were arrested after throwing stones and tables at Rangers supporters from a bar and firing Bengals at Rangers supporters and police.
- We hope that there will not be so many events like this, said Seville's mayor Antonio Muñoz this morning.
But an hour or so before kick-off, it was time again.
Hundreds of Frankfurt supporters were then seen attacking a couple dozen Scottish fans.
The fans are said to have thrown chairs and tables at each other, and some Rangers fans are said to have collapsed after the fights.
The commotion ceased when police arrived at the scene.
To date, no serious injuries have been reported.
The match is in progress.