Chelsea may lose their right on Bournemouth defender Nathan Ake if the Blues fail to exercise the buy-back clause.
Ake was sold to Bournemouth in 2017 in a move that saw Chelsea pocket £20million and he has risen to be one of the best defenders in the Premier League.
Chelsea will only sign the Dutch defender if Andreas Christensen seeks to quit the club this month.
Ake,24, has been seriously linked with a return to Stamford Bridge with the Blues having a £40million buy-back option and a first refusal right on the defender.
The Blues will not sign Ake unless Christensen is sold and manager Frank Lampard has ruled out a mid-season exit for the Dane defender.
The option of the first refusal will expire in the summer and if the Blues fails to make a move they will miss out on the defender if he opts not to seal a deal this winter.
Ake has been in scintillating form for the Cherries and his form has not gone unnoticed with the likes of Manchester City and other Premier League top clubs monitoring the situation.