Scans today revealed the 26 year-old Wallaby had torn his anterior cruciate ligament.
Robinson will undergo surgery in the coming days, which rules him out of the Tri Nations and the Rugby World Cup.
Wallabies coach Robbie Deans conceded the injury was a significant blow to Australia’s prospects.
“It’s disappointing news for Benn, disappointing news for the rest of the squad and for Australian rugby as a whole,” Deans said in a statement.
Robinson had been due to play his 43rd Test in Sunday’s clash with Samoa in Sydney but his injury may see either Western Force prop Pek Cowan or NSW Waratahs veteran Al Baxter to come into the 22-man squad.