Douglas Costa says he and his fellow players who are refusing to return to Ukrainian champion Shakhtar Donetsk do so because the conflict in the country puts their lives at risk.
Costa and five other South American players refused to leave France last weekend with the rest of the team to return to Donetsk for Shakhtar's first match of the season on Tuesday.
The players "all run a deadly risk if we are in the region," Costa said on his Instagram page. He said all six absentees wanted to train in Switzerland during the conflict, and were not seeking a transfer.
"I like the club, the people, the city, but I'm afraid," he said in comments posted alongside a picture of the Shakhtar badge. "We want to stay at the club, but we must have risk-free working conditions."
Costa, 23, has been with Shakhtar since 2010, winning five straight Ukrainian titles and reaching the Champions League quarterfinals in 2011.
Fellow Brazilians Alex Teixeira, Ismaily, Fred and Dentinho back Costa, along with Argentine striker Facundo Ferreyra. They represent less than half of Shakhtar's South American contingent, which also includes Brazil internationals Bernard, Ilsinho and Fernando.
UEFA has denied intervening in the situation after Shakhtar general director Sergei Palkin claimed to Russian agency R-Sport that UEFA "recommends that our players who have left the team return as soon as possible."
Palkin also said two of the missing players, Fred and Ismaily, would rejoin the team on Wednesday.
In a statement to The Associated Press, UEFA said its only communication with Shakhtar had been to discuss finding replacement venues for its home Champions League games.
"The communication did not reference the case of the six players," the organization said.
Costa's comments run counter to claims made by Shakhtar coach Mircea Lucescu, who has accused agent Kia Joorabchian of convincing the players they could use the conflict to sign new contracts with other clubs.
"It's a true scandal," Lucescu told French newspaper L'Equipe. "He took advantage from the situation to abduct them."
Shakhtar's billionaire owner, Rinat Akhmetov, has warned that the club could take legal action to force the six players to come back.
"If they don't come then in the first instance they will suffer," he said in a statement on Monday on the club website.
Refusing to fulfil their contracts could cost the players "tens of millions of euros" in compensation payments to the club, he warned.
The players did not return with the team following Shakhtar's friendly against Lyon on Saturday. Shakhtar plays a Ukrainian Super Cup match against Dynamo Kiev in the western city of Lviv on Tuesday.
Donetsk is held by pro-Russian rebels, who are battling advancing Ukrainian forces, and around 60 kilometers (38 miles) from the site where Malaysian Airlines flight MH17 crashed on Thursday with 298 people on board.
Shakhtar will play its home fixtures outside of Donetsk this season in one of four cities approved by UEFA as safe for European matches - the capital Kiev, Lviv, Odessa or Dnipropetrovsk.
No decision has yet been made, Palkin said, even though Shakhtar's first scheduled home game of the season is on Sunday.
Akhmetov's earlier preference was Kharkiv in the north east, which is majority Russian-speaking and held by the Ukrainian government, although there has been some unrest there in recent months.
The safety of players in Kharkiv was put in the spotlight after four players refused to return to the city's Ukrainian Premier League side Metalist Kharkiv, whose stadium Shakhtar would share under Akhmetov's plans.
The four players are Argentines Jose Sosa, Jonatan Cristaldo, Alejandro Gomez and Sebastian Blanco.
FIFA can impose strict penalties in breach-of-contract cases. Players can be suspended for four months and clubs can face a one-year transfer embargo which prevents them from registering and fielding any new signings.
As Ukrainian champion, Shakhtar has qualified for the group stage of the Champions League.
The Ukrainian Premier League season, which starts on Friday, has been reduced from 16 teams to 14 after its two Crimean clubs withdrew at the end of last season following Russia's annexation of the peninsula.
Besides Shakhtar, three other teams — Metalurh Donetsk, Olimpik Donetsk and Zorya Luhansk — are based in cities controlled by rebels. They will use stadiums in other cities.
Another club, Illichivets Mariupol, is based in a city claimed by the self-proclaimed Donetsk People's Republic but under Ukrainian government control.