Chelsea hope to complete the £35.1m signing of Tiemoue Bakayoko next week, but will face a battle to keep Nemanja Matic.
The Blues have agreed a deal in principal with Monaco for Bakayoko, who has been coach Antonio Conte's first choice target to strengthen midfield for several months.
Negotiations are set to continue over the weekend and personal terms have to be finalised with the France international.
But no complications are expected, with Chelsea prepared to offer him a five-year contract and a medical is planned for next week.
Bakayoko's arrival is likely o speed up the departure of unsettled Matic, who is a target for Manchester United and Juventus.
The Serbia international came close to leaving Stamford Bridge last summer only for Conte to block his departure.
Matic's form dipped in the second half of last season and is believed to have become frustrated that the club didn't offer him an extension to his current deal, which has two years left to run.
The 28-year-old has also seen his two closest friends at the club in Branislav Ivanovic and Asmir Begovic, who have joined Zenit St Petersburg and Bournemouth respectively.
The 28-year-old has also seen his two closest friends at the club in Branislav Ivanovic and Asmir Begovic, who have joined Zenit St Petersburg and Bournemouth
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Bakayoko has been earmarked to be the main partner for N'Golo Kante in midfield next term and Matic is prepared to move on.
Chelsea won't let him go on the cheap however, especially as Conte's plan is to add six signings to the squad that won the title so he has more strength in depth to compete in the Champions League, as well as the three domestic competitions.
Given Matic has helped Chelsea win the title twice in the last three seasons, it will take a minimum of £40m to convince the champions to sell him.