He later told the Herald that he was "absolutely" prepared to travel to the Czech Republic.
"It's really important for the integrity of our immigration system that this country knows what's going on. I think Iain Lees-Galloway has made a terrible decision around this, and if he's not transparent, we have to look at our options in Opposition."
Lees-Galloway earlier released the conditions around Sroubek's residency, which included not being convicted of any offence, not using any fraudulent identity, and not providing false information to a Government agency for the next fives years - starting from when Sroubek is released from prison.
"This is a very serious matter and I do not condone your behaviour," Lees-Galloway says in his letter to Sroubek.
"I have given you one final chance to remain in New Zealand and this should serve as a clear warning to you."
Lees-Galloway used his power of "absolute discretion" to cancel deportation liability and grant residence to Sroubek, who is also known as Jan Antolik.
Absolute discretion decisions are often the last option available for people to remain in New Zealand for cases outside ordinary immigration settings.
Lees-Galloway said he would not comment on the details of his decision because of privacy and legal reasons, "as is standard practice for all administrations".
"Any breach of these conditions is likely to lead to his deportation. As I have conveyed to him, I've given him one final chance to remain in New Zealand and live within our laws," Lees-Galloway said in a statement.
One factor thought to be taken into account is whether Sroubek's life would be in danger if he were deported.
It was also a factor after he was found guilty of using a false passport and lying to immigration officials in 2011.
Judge Roy Wade discharged Sroubek without conviction, convinced that Sroubek would be in danger from corrupt Czech authorities and the man he helped convict of murder if he were deported.
He added that Sroubek had made a positive contribution to New Zealand through his kickboxing prowess and business success.
Sroubek came to New Zealand from the Czech Republic in September 2003 to start a new life as Jan Antolik, after fleeing corrupt police who wanted him to lie and clear the main suspect in a murder investigation.
Instead, he left a videotaped witness statement which was later crucial in convicting the killer.
He fled the Czech Republic with a doctored passport but was unmasked in October 2009 when Czech police gave New Zealand police details of his identity and an arrest warrant on minor charges in connection with the 2003 murder.
Sroubek pleaded not guilty to the charges but admitted using a false identity to come to New Zealand.
His defence was he had a "reasonable excuse'' to give a false name as he had fled his homeland in fear of corrupt police officers and a criminal.
The Crown did not dispute his story but said Sroubek should have revealed his true identity to New Zealand authorities.
A jury convicted him, but Judge Wade gave him a second chance by discharging him without conviction.
Sroubek was jailed in 2016 for five years and nine months after being convicted of importing 5kg of MDMA with a street value of $375,000.
He appealed against that conviction last year, saying the MDMA was planted to frame him.
The Court of Appeal rejected his appeal.
Sroubek was also previously acquitted of committing an aggravated robbery with two members of the Hells Angels.
