Mr. Swiercz added that on Sundays — “as the law states” — Mr. Plaku had the day off.

A tribunal for Poland’s soccer federation ultimately dissolved Mr. Plaku’s contract with Slask Wroclaw but did not assign blame, which allowed the club to avoid paying Mr. Plaku the balance of his salary (about $222,000 in lost wages). Mr. Plaku has appealed, taking the matter to the Court of Arbitration for Sport, an international organization that adjudicates cases related to athletics. A decision is expected as soon as this week.

In Western Europe, accusations that clubs have treated players in a similar manner are common. Nicolai Boilesen, who was the captain of the Dutch club Ajax last season, was separated from the first team this year after refusing to sign a contract extension. Ajax’s coach, Frank de Boer, has been quoted as saying: “Nicolai made his choice. If you do not accept the offer that we make, then you have to suffer the consequences.”

In Eastern Europe, the problem is more pervasive. Results of a 2012 player survey conducted by FIFPro, the international players’ union, found that in 12 Eastern European countries, roughly one in six players reported having been forced to train alone, while about 40 percent of players in Poland specifically said they knew of at least one such incident.

Mr. Stefanovic, the Slovene player representative, said the survey offered only “a hint” of how common such intimidation tactics were. He cited the case of the Serbian midfielder Andrija Zivkovic, one of the continent’s most promising young players, who starred at the FIFA U nder-20 World Cup last year and was a centerpiece of the decorated team Partizan Belgrade.