Chelsea are reportedly willing to part ways with Marcos Alonso and Cesar Azpilicueta for £11m fees in the current transfer window.
Rudiger has already been unveiled as a new Real Madrid player, while Christensen is expected to sign for Barcelona, whose financial issues are currently holding up an announcement.
Thiago Silva will be remaining at the club for at least another 12 months, but Azpilicueta and Alonso both have just one year left on their respective contracts.
The duo are also rumoured to be on the radar of Barcelona, and Chelsea cannot realistically demand high prices for both defenders, who could leave on free transfers in 2023.
According to Sport, Chelsea are after a combined fee of £22m to part ways with the two Spaniards this summer, but the Blues could be persuaded to drive the price down.
The report adds that Azpilicueta and Alonso have both already reached agreements over personal terms with Barcelona and are hopeful that their moves to Camp Nou can be concluded next week.
The defensive pair would therefore be able to join up with Xavi's team for their pre-season tour of the United States, and Alonso's signing ought to be relatively straightforward.
However, Chelsea are supposedly prepared to drive a harder bargain for Azpilicueta, as Tuchel is pushing for the Blues captain to remain at the club for the new season.
The 32-year-old is understood to have informed Chelsea of his desire to leave after a decade at Stamford Bridge, during which time he has scored 17 goals and produced 55 assists in 474 games for the club.
Azpilicueta has won the Champions League, Premier League, Europa League, FA Cup, EFL Cup, Club World Cup and UEFA Super Cup during his 10-year spell and holds the title of being the Blues' current longest-serving player.
Meanwhile, 31-year-old Alonso has enjoyed a trophy-laden six-year spell at Chelsea since arriving from Fiorentina and boasts 29 goals and 23 assists in 211 outings for the London club.
Amid Ben Chilwell's long-term layoff, Alonso managed to reignite his Chelsea career under Tuchel and ended the 2021-22 season with four goals and five assists in 28 Premier League matches.
However, the left-back has confirmed his desire to return to Spain before he hangs up his boots, where he spent 11 years as a Real Madrid youth player before joining Bolton Wanderers in 2010.