The Brazilian did not have his best game on Wednesday night when Manchester City beat Arsenal 3-1 at the Emirates to move to the top of the Premier League table.
Arsenal have lost two of their last three league games and have not won a game in their last four in all competitions.
Their poor form has coincided with defensive frailties being exposed in recent games and Agbonlahor admitted that they again made crucial errors against the reigning champions.
However, he feels Gabriel is turning out to be a major problem at the heart of Arsenal’s defence and stressed that there is always a mistake in him.
The former striker insisted that the Brazilian was very lucky to not concede a penalty against Manchester City as well.
Agbonlahor said on talkSPORT: “A lot of mistakes from Arsenal.
“The first one, [Takerhiro] Tomiyasu, it happens. Jack Grealish was pressing him, he didn’t see Kevin De Bruyne running through but it’s Gabriel for me.
“Every time I am watching, he is one I think has got a mistake in him.
“Yesterday, the penalty, which was not given because of the offside but he got away with one there.
“He was fighting a battle with [Erling] Haaland and gives away a penalty.
“Then the goal that Haaland scores, it’s just poor defending all around.”
Arsenal are still level on points with Manchester City having played a game fewer than the champions.