During Sunday's home loss to Norwich, the 25-year-old left a female supporter needing paramedic treatment.
He apologised and sought out the victim to hand over his shirt as a souvenir at half-time.
Pieters also tweeted:
@kevantideswell sorry again for what I did.I didn't mean it. I hope she's ok and the shirt/this tweet shows you that I'm really sorry#stupid
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