The Magpies are set to make the 31-year-old England international the first signing of Saudi Arabia’s Public Investment Fund consortium since their takeover last year.
Newcastle have agreed a £12m fee with Atletico Madrid and Trippier is already in England undergoing a medical.
Agbonlahor reckons Man United do not have enough quality from their right full-backs, and Trippier's addition would have been a step up.
“When I watch Man Utd, [Cristiano] Ronaldo must be so frustrated from the right-hand side. I love Wan-Bissaka defensively – but he can’t cross a ball," the former Aston Villa striker told TalkSport.
“There was an incident [against Wolves] where he tapped the ball with his left foot and fell over and crossed it out of play.
“He’s just not good enough for United’s service.”
“I don’t understand, why have Man Utd let Trippier go to Newcastle? He would be perfect,” he added.
“Put him on the right-hand side. Imagine how many goals Ronaldo and Cavani would get from that service.
“Wan-Bissaka is not a modern-day full-back, especially not in a modern-day team. So, for me, United have missed a trick with Trippier.”
