Plummer stepped in to replace Kevin Spacey when the "House of Cards" star was edited out of the film amid a sexual misconduct scandal, and went on to land an Oscar nod for his portrayal of billionaire J. Paul Getty.
Scott released a statement following the news of the actor's death, which read, "I was fortunate enough to work with him less than 2 years ago and had a wonderful experience. My heartfelt condolences go to (wife) Elaine. He will be really missed."
Plummer's "Knives Out" castmate Chris Evans was also quick to pay his respects, tweeting, "This is truly heartbreaking. What an unbelievable loss. Few careers have such longevity and impact. One of my favorite memories from Knives Out was playing piano together in the Thrombey house between set ups. He was a lovely man and a legendary talent."
Rosanna Arquette, Dean Norris, Rosie O'Donnell, Joseph Gordon-Levitt, and filmmaker Edgar Wright have also posted Twitter tributes to the late Canadian star, while Dana Delany recalled seeing Plummer onstage. "Christopher Plummer was always interesting and in command, but never afraid to reveal the depths," she wrote.
Meanwhile, a statement released by the Academy of Motion Picture Arts & Sciences reads, "Christopher Plummer beguiled audiences across generations in memorable roles from Captain von Trapp in 'The Sound of Music' to Harlan Thrombey in 'Knives Out'. He worked steadily for 60+ years, winning a Best Supporting Actor Oscar in 2012 for 'Beginners'. He will be missed."
Plummer passed away at his home in Connecticut.