Hakeem Al Araibi, who lives and plays in Australia, was arrested in November in Bangkok on an Interpol notice issued at Bahrain's request.
The Australian soccer players' union has already asked the Asian Football Confederation (AFC) to intervene to help secure his release from prison in Thailand.
Araibi, who played for Bahrain's national soccer team and was a critic of the government, had been convicted of vandalising a police station and sentenced to 10 years in prison in absentia.
He denies wrongdoing. The Bahrain government says Araibi can appeal against the sentence if he returns to the kingdom. Araibi was granted asylum in Australia in 2017 after fleeing Bahrain three years earlier.
FIFPro said it was calling on footballers "to help a fellow player", detailing measures such as signing an Amnesty International petition.
"The clock is ticking and we ask all footballers to do what they can to #SaveHakeem," it said in a statement. "He must be allowed to return to Melbourne, where he is a player for Pascoe Vale FC, and be allowed to live in peace."
It said Araibi travelled to Thailand with his wife to celebrate their honeymoon and was now "trapped in a crammed cell."
Araibi was a vocal critic of AFC President Sheikh Salman bin Ebrahim al-Khalifa, a member of Bahrain's ruling family and cousin of the king, when he contested the FIFA presidential election in 2015.
FIFPro said it was "deeply concerned about his (Araibi's) safety, and the manner in which Asian football authorities... have remained silent on the matter."
Meanwhile, FIFA said it had been in regular contact with the AFC over the issue. FIFA has "been working behind the scenes and... been in regular contact with our national associations and with the AFC about this case," a spokesman said late on Tuesday.
Last week, the governing body said Araibi should be freed and allowed to return to Australia to continue his career.
The AFC has said it was working with groups including FIFA, but declined to comment further.
(Reporting by Alexander Cornwell and Brian Homewood; Editing by Amlan Chakraborty, Alison Williams and Toby Davis)
