LONDON - Chelsea striker Diego Costa has been left out of the squad to face Leicester on Saturday (Jan 14) after a row with a club fitness coach, according to reports.
The Spain international has not trained this week and has not travelled for the Premier League leaders' match with the defending champions, said the BBC.
The news comes amid reports he is the subject of an offer to move to China that would be worth £30 million (S$52 million) a year.
Costa, 28, has been in superb form this season and is the league's top scorer with 14 goals, said Sky Sports.
According to sources, Costa has become unsettled by the approach from China, which would make him one of the highest paid footballers in the world, said Sky.
Chelsea has declined to comment.
It is understood that Blues owner Roman Abramovich is not interested in releasing him from his contract, which expires in 2019, and would not entertain the idea of being forced to do so, said the BBC.
Speaking in early January, Costa admitted he wanted to leave Chelsea last summer, but said he was now happy to stay.
Chelsea had been hopeful of agreeing a contract extension with the Brazil-born forward, but the dispute with fitness coach Julio Tous raises new doubts.
Costa joined the Blues for £32 million in 2014, and was understood to be close to a return to former club Atletico Madrid after a difficult 2015-16 campaign.
"Did I want to go? Yes, yes, I was about to leave," he said earlier this month.
"But not because of Chelsea.
"There was one thing I wanted to change for family reasons but it wasn't to be, and I continue to be happy here."
It comes as a major blow to Chelsea as the Premier League leaders look to get their title bid back on track at the King Power Stadium on Saturday evening, following defeat to Tottenham last week, said the BBC.
Sky Sports football expert Graeme Souness believes this could derail Chelsea's title bid.
"This is the very last thing Chelsea need. He is playing out of his skin. They lose him and all of a sudden they are not going to win the Premier League," Souness said.
"If sense prevailed, maybe he could stay until the end of the season. There has to be a way around this where everybody can be happy."
Costa has scored 50 goals for the Blues in all competitions.