Onana was a second half substitute at a time when Manchester United were trailing 2-1 and took exception to Maguire gifting possession in a dangerous area which nearly resulted in a goal.
After rescuing the dangerous situation, Onana went straight towards Maguire to let his feelings known.
The Cameroon goalkeeper was playing his second pre-season game for Manchester United after joining from Inter Milan as David De Gea's replacement last week.
Maguire was recently stripped of the Manchester United captaincy by manager Erik Ten Hag and his future at the club is in doubt.
Speaking as a pundit on TalkSport, former Aston Villa and England striker Gabriel Agbonlahor felt Maguire is being scapegoated for everything bad about Manchester United.
“First of all Harry Maguire did nothing wrong,” Agbonlahor told talkSPORT.
“He gave the ball to a midfielder, who gave it away, and I feel like he is an easy target. I don't like that from Onana - I felt like he (Maguire) is an easy target.
“Are you doing that to [Lisandro] Martinez? I don't think you are, or even [Marcus] Rashford like that? Maguire is an easy target, so I did not like the look of that. I would understand if it was a big mistake and cost a goal or it was Harry Maguire's fault, fair enough. But I want to see that same energy from every player.
“I understand he (Onana) is trying to create high standards but, when you watch games with him, he has given the ball away a lot and made mistakes. Imagine Harry Maguire doing that to him. I feel like you need to respect your team-mates.”
