The Brazilian-Spanish striker was dropped by Antonio Conte from the squad that is facing Leicester on Saturday as he has reportedly have a row with the Italian manager.
The root of the issue appears to be an exuberant offer from a Chinese club. Souness warned the London club that the rift has to be repeared as soon as possible.
"This is the very last thing Chelsea need," the pundit said on Sky Sports News.
"He [Costa] is playing out of his skin.
"They lose him and all of a sudden they are not going to win the Premier League.
"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."