Brüssow set to miss Saints' trip to Newcastle
The South African flanker was forced off after just 13 minutes in the recent Anglo-Welsh Cup semi-final defeat at Bath.
Brüssow sustained a hamstring injury and has not been training this week.
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Hide AdInterim head coach Alan Dickens said: "Heinrich Brüssow is struggling.
"He came off with a hamstring injury and he hasn't been training this week."
Courtney Lawes will also miss out after being sidelined for the remainder of the season with a knee injury sustained during England's Six Nations defeat to France in Paris.
"It's s shame because Courtney's been one of our stand-out performers this season," Dickens said.
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Hide Ad"Week in, week out, he's been fantastic and it's a shame he won't be able to see the last five games out.
"We wish him a speedy recovery.
"Everyone else who has come back from international duty is ready to play."
Teimana Harrison is absent as he serves a one-week ban for his sending off at Bath.
Prop Alex Waller continues to recover from the broken arm he sustained against Newcastle back in December.
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Hide Ad"Alex Waller is due to go and see the specialist this week," Dickens said.
"He's training but not rugby training, chucking the ball about.
"He's had a week off as part of his rehab and fingers crossed for good news this week."