James McClean has had abusive packages sent to him at Stoke's training ground over his refusal to wear a poppy, says club manager Gary Rowett.
The 29-year-old Republic of Ireland international was the subject of abuse from home and away fans during last weekend's home draw with Middlesbrough.
And he has spoken about receiving death threats in the past over the issue.
"He's been sent stuff which I've seen," Rowett said. "You can understand in a way why he reacts. He's only human."
Earlier this week McClean was warned by the Football Association after his use of an offensive word in a social media post in which he called some Stoke fans "cavemen".
He has previously explained why he does not wear a poppy, and Stoke issued a statement confirming his stance had not changed.
Speaking to BBC Sport Rowett said: "When you have those beliefs you appreciate that it's going to be a big situation at the weekend like that.
"We spoke to James about it and I think his response was out of frustration, probably ill-judged.
"Certainly criticising a minority of our fans is not the way to go and we spoke to him about that. We can't condone that but I think when you understand the background to his beliefs and you see that his family have had death threats, you see that his wife and kids have had abuse constantly, you see that he's been sent stuff in the post, which I've seen recently from fans and you can understand, in a way, why he reacts.
"We can't condone certain parts of those actions but we can understand some parts of it because the abuse is pretty pretty bad. We will try to move forward. The club have spoken to James about it. It's certainly not something that we want to condone."
The Professional Footballers Association has said it had offered its support and assistance to McClean following "the unacceptable abuse he has received".
"The poppy symbol is an important recognition of the sacrifice so many made in the World Wars in the UK however it should always remain an individual's choice whether or not to wear it," the PFA said.
"There is no justification for the abuse he and his family have received for his beliefs and he should be supported in the same way as any other player who receives abuse based on his or her race.
"We call upon the other stakeholders in football to recognise this and support an individual's right to express his personal and religious beliefs without fear of threats and abuse."