Arsenal defender Myles Lewis-Skelly was substituted 34 minutes into Arsenal's Champions League last-16 first leg fixture with PSV after 'getting away with one' in the first half.
The 18-year-old received a yellow card in the 24th minute for pulling back Luuk De Jong, and just minutes later tripped Richard Ledezma down the PSV right.
PSV players and fans called out for a second booking from Spanish referee Jesus Gil Manzano, but the official kept his cards in his pockets and allowed the teenager to continue playing.
Gunners boss Mikel Arteta wasn't willing to take a chance however, even until half time.