Shakhtar Donetsk midfielder Douglas Costa says he and his fellow players who refused to return to the Ukrainian champion did so because the conflict in the country puts their lives at risk.
Costa and five other South American players refused to travel with the rest of the team to Ukraine for Tuesday's first match of the season.
The players ''all run a deadly risk if we are in the region,'' Costa said on his Instagram page. He said he and the other five absent players 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 2010-11.
The city of 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 Thursday with almost 300 people on board.
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 to Ukraine.
''If they don't come then in the first instance they will suffer,'' he said in a statement Monday on the Shakhtar 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 Donetsk's friendly against French team Lyon on Saturday. Shakhtar plays a Ukrainian Super Cup match against Dynamo Kiev in the western city of Lviv on Tuesday.
As well as Costa, fellow-Brazilians Alex Teixeira, Ismaily, Fred and Dentinho have not reported back with the club, along with Argentine striker Facundo Ferreyra.
The six represent less than half of Shakhtar's large South American contingent, which also includes Brazil internationals Bernard, Ilsinho and Fernando.
Shakhtar will play its home fixtures outside of Donetsk in the coming season, with Akhmetov expressing a preference for the nearby city of Kharkiv, 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 has been put in the spotlight after a total of 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 all Argentinian, named as Jose Sosa, Jonatan Cristaldo, Alejandro Gomez and Sebastian Blanco in Argentine media.
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 this season's Champions League.
The Ukrainian Premier League season, which starts 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 because of the conflict.
Another club, Illichivets Mariupol, is based in a city claimed by the self-proclaimed Donetsk People's Republic but under Ukrainian government control.
New Crimean clubs have been created since the Russian takeover, but have yet to be admitted into the Russian league system.
Last week, UEFA announced it would keep Ukrainian and Russian clubs from playing each other ''until further notice'' because of the continuing unrest.
The ruling meant that Russian side Zenit St. Petersburg and Ukrainian club Dnipro Dnipropetrovsk cannot be paired against each other in the Champions League qualifying draw.
UEFA said the turmoil would not prevent matches from being played at home by Dnipro and Chornomorets Odessa. UEFA also said a security assessment showed that Lviv and Kiev can continue to host matches.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports).