Majchrzak confirmed to the New York Post that Szczerek is the man in the video, and revealed he sponsors his tennis federation in Poland.
Furious internet users have been quick to blast him for his alleged actions.
“Only an ordinary idiot and a jerk could snatch a hat from a child’s hands,” said one commenter.
Another said: “If the company’s president so unscrupulously stole a child’s hat, if I were a customer, I would no longer use his services.”
A shocking scene played out after Brock watched Majchrzak score the biggest win of his career against Karen Khachanov on Thursday.
The 29-year-old Pole was filmed removing his cap and trying to hand it to Brock, who was stood in the crowd.
Yet a brazen onlooker stood next to the boy swiped it instead and quickly stuffed it into his bag.
The kid looked devastated as the man took off with the hat, while Majchrzak hadn’t noticed the shocking moment.