The German side eliminated Benfica in the previous round, losing 4-2 in Portugal before a 2-0 win at home.
Sarri is wary of Frankfurt’s intensity and admits it will be difficult for his side to get past them.
“I respect Frankfurt. They have played against big teams and are a dynamic team with a great intensity and physically with the same characteristics as Prague, but the quality is better, especially offensive.
“So it will be difficult to get to the final,” Sarri told a press conference on Wednesday.