Speaking exclusively to Football Insider, the ex-Aston Villa and England attacker suggested being dropped against Crystal Palace last week can serve as motivation for Willock to rediscover his best form.
The midfielder scored eight goals in 14 Premier League games last season after signing on loan from Arsenal.
Newcastle made the move permanent for a £25million fee over the summer but he is yet to find the net this term.
According to WhoScored, the attacker has managed just seven shots in eight top-flight games this season.
The 22-year-old was dropped to the bench by interim manager Graeme Jones at Crystal Palace last weekend.
“Willock’s a shadow of the player he was last season on loan,” Agbonlahor told Football Insider correspondent Connor Whitley.
“Signing on a permanent deal after being on loan, that can happen sometimes.
“But I’m hoping he can improve his game. He’s a quality player and it hasn’t worked for him this season.
“I’m sure when he forces his way back into the team, he will show why Newcastle bought him because he’s a quality player.
“Sometimes you can have a slow start to the season and get better.
“Being on the bench for the Crystal Palace game, he’ll want to get back into the side. He’ll know that he won’t just walk back in, he’s got to work for it.”
The former England youth international played 78 times for his boyhood club Arsenal before his move.