The two players suffered injuries during South Africa’s hard-fought 23-19 quarterfinal win over Wales at Twickenham on Saturday.
Du Plessis’ hand was accidentally stamped on by teammate Francois Louw while second-rower De Jager has a foot injury.
No one has made more tackles at Rugby World Cup 2015 than De Jager (60) and he has formed an intimidating second-row partnership with Eben Etzebeth since the Springboks lost Victor Matfield to injury.
“Lood has injured a tendon in his foot so we need to give him some time to see how that settles and we will make a decision later in the week on his availability for the All Blacks game,” team doctor Craig Roberts said.
“Bismarck has a nasty laceration to his right hand. Flo (Louw) accidently stood on his hand, luckily no fracture, but it is a bit sore and swollen for him so we will keep an eye on him throughout the week.”
The 38-year-old Matfield, who injured a hamstring in the 46-6 win over Samoa in South Africa’s second pool match, is still recuperating and not regarded as fit enough to resume playing yet.
“Victor (Matfield) has been doing really well with his rehab, (but) when you’re older it takes a lot longer for you to recover. He has been working really hard and progressing nicely but will have to see nearer the end of the week,” said Roberts.
Backrower Louw believes the Springboks have enough strength in depth to cope should Du Plessis and De Jager not regain full fitness.
“They are both immense players,” said Louw. “Lood presents himself massively on the field in our defence, he will be a big loss should it go that way, and so will Bismarck.
“It is a concern but the Springboks have great depth in the squad and that’s vital in a World Cup. Adriaan (Strauss), and Pieter-Steph Du Toit can really enter the team should Victor not be ready. We have the players to cover if necessary.”
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– African News Agency (ANA)