Ten Hag is fighting to avoid the sack after United's worst start to a top-flight season since 1989-90.
Frank's side travel to Old Trafford on Saturday sitting three spots above United, who are languishing in 14th place after just two wins from their first seven league games.
A loss to Brentford would push Ten Hag closer to the axe, but Frank is convinced the Dutchman does not deserve such intense scrutiny,
"It's incredible how much scrutiny he's had to face," Frank said. "As a head coach, I acknowledge how it feels to be in a situation like this. I think the criticism is too much.
"He's clearly a good coach, he's won two trophies in two seasons.
"But I understand how it is: if the team wins, the head coach is absolutely fantastic; if the team loses, the head coach is absolutely s**t! Whereas it's probably somewhere in between.
"It's never only the head coach, or the players, or the fans, or the board, it's a combination of all of these things."
Frank claimed he will disregard United's recent results, even though they have gone five games without a win in all competitions.
"I've experienced it too many times in my career: we face a team that has lost three games in a row but they come out absolutely flying," he said.
"I don't really pay too much attention to form. I believe that we can go anywhere and beat any team, but I'm also aware that, when we go to Old Trafford to face Manchester United - a massive club with top players - they are favourites.
"But we need to go there with the approach and mindset that we can win."
