Two players of football club Chelsea -- Diego Costa and Oscar -- got into a brawl during a team training session on Wednesday.

SkySports reported that the duo were restrained by some of their teammates when Oscar performed a "strong tackle" on his teammate's knee while they were training at the team's base in Cobham, United Kingdom.

A Telegraph source, who witnessed what happened, recounted that Oscar's "outrageous challenge" happened after Costa also went hard on him earlier in the training.

"Oscar's was straight into the knee of Costa and could have done him some real damage. That sparked a brawl between them and the other players had to stop it," the source added.

It was noted in the SkySports report that the misunderstanding did not end up with punches being thrown at each other, as they were immediately separated during the altercation. 

According to Telegraph, Costa is the player who would easily lose his temper during games, but it noted that the incident was largely blamed on Oscar this time.

Costa previously received a retrospective FA ban after he lashed out a Laurent Koscielny and threw a bib at former manager Jose Mourinho's direction when he was dropped.

They have reportedly settled their differences and even walked off the field laughing.

The team has not yet released a statement on the incident, but Independent said it will be one of the issues to be discussed at the club's press conference on Friday. The team event will be led by interim manager Guus Hiddink.

This is said to be not the first time that a bust-up happened in Chelsea's roster as Charly Musonda also got involved in a similar incident before Mourinho left the team.

Meanwhile, Oscar wanted to soften the issue on his Twitter account saying: "For those who are talking to me and @diegocosta struggle today in training he's lying, he's one of my best friends and never fight."

According to The Guardian, the Chelsea duo has been together since their team struggled to perform well, but it claimed that they have shown improvement since Hiddink replaced Mourinho last December.

It even noted that they were very prominent players during Chelsea's 3-0 victory at Crystal Palace on Sunday.

This bust-up, as per Daily Mail, is an "unwanted headache" for the team as they go against Scunthorpe this weekend for the FA Cup.

The FA Cup third round will happen at Stamford Bridge on Sunday.