The Belgian club are set to take on Aston Villa in the Champions League group stages.
Villa have won all their group stage games so far, beating Young Boys, Bayern Munich, and Bologna.
“I think there is still a minimal difference with the real top clubs in England, but it is true that Aston Villa competes for the prizes every year,” Mignolet, who previously played for Liverpool, told reporters in Belgium.
“It is a completely different match than in the league. It will be much more open. We're going to find ourselves in a completely different scenario against Aston Villa.
"Villa have proven to be a stable and competitive team in recent years. I know from experience that even the lowest in the Premier League can be a tough opponent. So it certainly won't be an easy game."