Chelsea will reportedly be required to sell one of their defenders if they wish to secure a reunion with Nathan Ake.
When the Blues sold Ake to Bournemouth in 2017, they inserted a £40m buy-back clause, which must be activated by the end of the current transfer window.
Given his side's issues at the back, Frank Lampard has been tipped to bring the former academy graduate back to Stamford Bridge.
However, The Sun claims that the West Londoners must first free up space on their wage bill before being able to sign the Netherlands international.
AC Milan allegedly hold an interest in the Dane, although the Italian giants may only be prepared to commit to a loan deal.