The Shakhtar Donetsk midfielder Douglas Costa says he and his fellow players who refused to return to the Ukrainian champions 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. Costa’s fellow Brazilians Fred, Dentinho, Alex Teixiera and Ismaily, and the Argentinian striker Facundo Ferreyra, also remained in France following a friendly against Lyon on Saturday.

The city of Donetsk is held by pro-Russian rebels who are battling advancing Ukraine forces, and lies around 38 miles from the site where Malaysian Airlines flight MH17 crashed on Thursday with almost 300 people on board.

Costa’s comments run counter to claims made by the Shakhtar coach Mircea Lucescu, who has accused the 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.

Shakhtar will play their 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 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 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 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.