The 23-year-old picked up the injury in his left knee after falling awkwardly in the 54th minute of Friday's 0-0 friendly draw against Dutch side Vitesse.
HSV sporting director Oliver Kreuzer confirmed the following day that Beister had flown back to Hamburg for further medical examinations and surgery on the affected knee. "He'll have the operation and begin his rehabilitation in the coming weeks, but we're looking at six or seven months before he can start playing again," said the 48-year-old to hsv.de. "It's a difficult situation for all of us and obviously extremely disappointing."
Beister has been a key player for HSV in the current campaign, having scored five and set up as many goals in 16 Bundesliga outings so far this term. In light of his injury, and the recent departure of striker Artjoms Rudnevs to Hannover 96 on loan, Kreuzer also confirmed that the club may look into signing reinforcements before the end of the January transfer window. "We'll have a conversation about what we can do, but we've lost two players now. So we'll be keeping our eyes open for any possible opportunities in the transfer market."
You can watch highlights of Hamburg's draw against Vitesse courtesy of the official Bundesliga YouTube channel: