The Spain striker had an unhappy 2015/16 season and Madrid-based newspaper AS claim he's told owner Roman Abramovich and manager Antonio Conte of his decision to depart Stamford Bridge.
Costa is expected to feature for Chelsea in their first match of pre-season against Rapid Vienna tomorrow.
The France midfielder has been linked with a move after his pivotal role in their Premier League title win last season.
And French outlet RMC Sport say a £30million fee has been agreed between the two sides and Kante will sign a five-year-deal with a medical set to take place in the next 48 hours.
The Greece international is understood to be one of Antonio Conte's top defensive targets but the Serie A side are reluctant to let him go.
But Italian newspaper Il Messaggero claim Roma are struggling to convince Manolas to stay, with the 25-year-old seeking an increase to £48,000-a-week from his current £22,500-a-week salary.
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