The German forward, 21, will undergo surgery this week as he becomes the latest name to join Brentford's injury list.
“It’s a blow, of course it is. He’s a player we have big expectations for, and he was starting to show some of his fantastic abilities with a goal against Crystal Palace.
“But this is football; this happens. There will be challenges that we have to work our way through, and we will do that.”
He's played 23 times in the Premier League for the Bees, scoring one goal and providing an assist.
Schade's goal against Palace on 26 August was later nominated for August's Budweiser Goal of the Month.
In addition to Schade being ruled out, Frank confirmed that he has several players unavailable through either injury or suspension.
“Every team has injuries, and with Ivan Toney’s ban included we have seven players out,” Frank added.
Brentford are in EFL Cup acton on Wednesday against London rivals Arsenal, looking to end their two-match losing streak.
The Bees then take on Nottingham Forest at the City Ground on Sunday.