The Frenchman also feels Liverpool can rise at any time under Jurgen Klopp as the German battles to find consistency at Anfield.
Benteke has struggled for goals since his Â£32.5million summer switch from Villa, netting just seven in 30 games for the Reds.
He scored 49 goals in 101 outings during a three-year spell at Villa and helped save them from relegation last season.
But despite Benteke's struggles for his new club Garde insisted he will be a danger ahead of the Belgium international's first return on Sunday.
He said: "I know he is a tremendous goalscorer
He has been in this position last season and probably helped Aston Villa a lot to be safe.
"When you play for a new team it is always difficult to settle in
I just know that he's threatening players if he is playing, anywhere and anyhow, whether he's been playing well or not in previous weeks.
"I know that when you're back at the club you played for for a long time it's something special for players
We will have to be careful and aware of about him."
Liverpool are ninth in the Barclays Premier League with Villa bottom and eight points from safety despite last week's 2-0 win over Norwich.
Klopp has won 12 of his 29 games in charge at Anfield and Garde predicted they will improve under him.
He added: "I'm not too comfortable with teams that are not in a good mood because they will wake up, especially a club like that; especially a team with threatening players up front.
"They have the choice, they have the quality and they have the quantity up front.
"We know that it is going to be difficult
It's up to us to leave them in the mood that they are in the moment."
Source : PA