The 26-year-old is a key figure for the Premiership club, having made 128 appearances since earning his debut in 2009, but he now looks set to miss the start of the 2017-18 campaign.
Wallace dislocated his hip during Saturday's pre-season victory over London Irish and was taken to hospital after a brief assessment from the club's medical team.
Harlequins have now confirmed that he will need to go under the knife to correct the issue and they are unsure how long it will keep him on the sidelines.
Meanwhile, the club have also passed on their best wishes to academy winger Jonas Mikalcius, who underwent surgery on his left knee last week.
Harlequins Director of Rugby John Kingston told the club's official website: "We are all wishing Luke and Jonas the very best for their recovery.
"The road back to full fitness will be a long one, but they are both very resilient characters and I know they will be determined to do all that they can to come back stronger."