For Bees midfielder Onyeka, it was his first taste of English football, albeit in a non-competitive nature.
He took a hefty whack from United midfielder Garner with not much of the contest remaining. He required treatment on the pitch, but did manage to soldier onto the end of the contest.
"You know I'm Frank 'The Tank', so of course few days it's going to be fine, it's just a little pain so nothing to worry about," Onyeka told Brentford's club website.
"I love a tackle, actually I gave one before I got one, so it's normal for me when I get tackled. I think the guy (Garner) was pretty hard on me."
On his first experience of playing in England, especially when getting the chance to do that at Old Trafford, he added: "It was good to get my first minutes, it was amazing playing in Old Trafford, watched Old Trafford on television and I get to play yesterday. It was pretty and a good experience for me as well.
"It was pretty intense and the pace of the game was high, it was really fast. At some point it was difficult to get along but that's how it is in the Premier League."
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