Violence following a pre-season friendly involving LeedsUnited has resulted in 25 arrests and seven injuries.
The fighting broke out in the Austrian town of Eugendorf after the match between Leeds and Eintracht Frankfurt, which the German team won 2-1.
Austrian police said about 50 Frankfurt fans stormed the stadium entrance and injured security staff on Tuesday night, while fans from both clubs fought on the field after the game.
Clashes later continued outside the ground and police used pepper spray to separate the rival groups.
Three Leeds supporters and two police officers are reported to be among those injured.
Around 450 Leeds fans travelled to Austria for the match, according to local authorities, along with 300 from Frankfurt. The total attendance at the games was 1,100 spectators.
Riot police were deployed during violent scenes in Salzburg and Eugendorf before kick-off.
Supporters from both clubs were arrested, 17 of which were from Frankfurt, after confrontations between the rival fans on the pitch at full-time.
Pepper spray was used to control a group of Frankfurt fans following trouble in Eugendorf town centre after the game, Salzburg police have confirmed.
Fighting on the pitch after the game spilled over into the square in front of the stadium where mounted police are reported to have intervened.
A police statement said: "At the square in front of the stadium, runaway Leeds fans were again attacked by the Frankfurt fans.
"Eventually the situation moved to the centre of Eugendorf where action was taken to stop the attacks, among other things a pepper-spray operation by the police."
It was also reported that police had been forced to intervene earlier in the day after around 50 Frankfurt fans had refused to pay the bus fare following their journey from Salzburg to Eugendorf.
Salzburg police have not confirmed the severity of any of the injuries caused.
Leeds had arrived in Eugendorf at the weekend for a week-long training camp and will now head to Norway for a friendly game against another German side, Hoffenheim, in Lillestrom on Saturday.