Chelsea welcome PSG to Stamford Bridge for the second leg of their UEFA Champions League last 16 tie on Wednesday, with the fixture finely poised after a 1-1 draw in Paris in mid-February.
Mourinho was unhappy with the treatment dished out to Eden Hazard at the Parc des Princes, with just two PSG players being cautioned despite the Belgium star being fouled a record nine times throughout the game.
"The most agressive team we've played this season is Paris Saint-Germain," the Chelsea boss said.
"I have to be fair, I thought an English team would never be surprised by aggressive play because we have it in our country.
"We've played against sides from the Championship in the Cup, against teams from League One and Shrewsbury [Town] from League Two, but the most aggressive team was PSG.
"For me, that was a real surprise. With players of such quality, I was expecting more football and less aggression."
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