But his soccer allegiance can vary, depends on which English Premier League team is playing well, and this revelation did not sit well with Bombers great James Hird.
"Wash your mouth out" was Hird's reaction when young Pennicott conceded he likes Manchester United, as well as their hated rivals Liverpool.
Setting aside that strong disagreement, Hird was happy to be on hand to help support Pennicott and another former Essendon captain, Dyson Heppell.
Pennicott is 13 and has the rare autoimmune disease Scleroderma.
Heppell's grandmother had the same condition and that prompted him to become an ambassador for Scleroderma Victoria, which is how he met his young mate Harrison.
Much in the same way that Neale Daniher has become the face of the campaign to find a cure for motor neurone disease, Heppell and Pennicott have teamed up to raise awareness for Scleroderma.
Along with Heppell's wife Kate Turner-Heppell, they now have the Haych clothing brand and a pop-up store in Melbourne for grand final week.
"I've had an incredible journey with the boy so far. He's in good spirits and quite healthy at the moment, which is incredible," Heppell said of Pennicott.
"We've had a lot of support, a lot of fun.
"That's been the most incredible thing, the connection with my grandmother - raising a lot of awareness for Scleroderma."
Hird, now a media commentator, turned up to the media opportunity in a suit while everyone else was wearing Haych clothing.
"Obviously I'm not cool enough to get the merch," Hird joked.
"I'm here to support H and help him live out his bucket list, but also raise awareness of the disease.
"It's so close to 'Hep' and his journey - anything I can to help promote it.
"He (Pennicott) is a great man, doing a great job through a lot of adversity."
Pennicott has done a lot with Heppell over the past few years, but his next goal is big.
"I really want to meet Cristiano Ronaldo," he said.
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