Antonio Rudiger had to undergo knee surgery this week after limping out of last weekend's Premier League clash with Manchester United, while veteran Gary Cahill is also out.
It leaves Sarri with only David Luiz and Andreas Christensen to use at the heart of defence. Cesar Azpilicueta is also an option, but the versatile Spaniard has typically only played centrally in a back three and has been more used to operating at right-back this season.
"We are in trouble with the centre-backs," Sarri is quoted as saying by BBC Sport.
The Chelsea boss estimates that 33-year-old Cahill could return in 'one week', while Azpilicueta has been preparing as a centre-back in training 'just in case' he is needed.
"We were lucky previously but not in the last 10 days," Sarri explained.
"Christensen has played about 25 matches during the season so he is ready. I hope he will be very fresh, mentally and physically. I am really confident with Andreas. He's played very important matches very well so he isn't the problem. The problem is the numbers."
Christensen has been much less involved under Sarri this season compared to former manager Antonio Conte last season. The Danish international featured in all but 11 of Chelsea's Premier League games in 2017/18, yet has only featured in seven this season.
Christensen has been a regular in the Europa League, however, starting all 12 games so far.
Brazilian winger Willian had also been a doubt for the game in Frankfurt after being on the receiving end of a reckless tackle from Manchester United defender Marcos Rojo on Sunday, but he appears likely to be involved after being able to train on Wednesday.
Callum Hudson-Odoi is a long-term absentee after suffering an Achilles rupture.
Source : 90min