Luiz played a vital role in the Blues' successful 2016/17 Premier League campaign, but was dropped after the 3-0 loss to Roma in the Champions League at the end of October.
Christensen has replaced him since then and helped Chelsea to a 1-0 win over Manchester United, as well as a 4-0 victory at West Brom.
However, Luiz returned to the starting lineup for Wednesday evening's 4-0 thumping of Qarabag, meaning Antonio Conte has a decision to make as to who plays against Liverpool this weekend.
"David came back in and performed well," Cahill said. "Andreas is a younger version of him if you like. I feel like David can offer Andreas a lot of help in his progression. He has been there and done it at the top, top level, he has won many trophies.
"David is a very experienced defender and Andreas' attributes are very similar. I feel that he (Luiz) can advise him tremendously and he has done up until now."