The Dutchman was carried from the field after 13 minutes of Sunday's 1-0 defeat to Napoli, having previously attempted to play through the pain, and reports surfaced on Monday that scans had shown a tear to the anterior cruciate ligament in his knee.
Strootman seems certain to miss Roma's remaining 12 Serie A fixtures as Rudi Garcia's charges look to cement second place and a return to UEFA Champions League football.
It also seems likely he will be absent for Netherlands' entire World Cup campaign in Brazil after starting nine of his country's 10 matches in qualifying.
National coach Louis van Gaal was deeply sympathetic towards the 24-year-old, and lamented the news dealt to the Netherlands squad.
"This is dramatic for Kevin," he told the Dutch Football Association's (KNVB) official website.
"I can imagine that his world right now just collapses. This is a loss, Kevin played a very big part in our qualification for the World Cup in Brazil.
"It's terrible for Kevin, who sees his dream fall in tatters."
Netherlands already face a tough task in Brazil having been drawn alongside Spain, Chile and Australia in their group.
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