The 27-year-old Olympic medallist was admitted to hospital in Perpignan, France last week after falling ill during a training camp but her health has since deteriorated.
The KNSB said Van Ruijven's condition has not improved after undergoing surgery twice and remains in intensive care.
Speed Skating
Schulting makes history with superb all-conquering display at Short Track World Championships
"Lara is currently fighting for her life," Dutch short track coach Jeroen Otter said in a statement.
"With incredible perseverance she has won the world title on the ice, but this battle is many times tougher.
"We all sympathise with her and hope with all our heart that she will come out well."
Van Ruijven won the 500 metres world title at the championships in Sofia last year, and an Olympic bronze medal in the 3,000m relay at 2018 Pyeongchang Games.
Speed Skating
Schulting bags double gold at Short Track World Championships
Speed Skating
Brilliant Van der Poel shatters world record to claim second world title of the week in Heerenveen
14/02/2021 AT 19:38