The cursed Leicester centre, who was only one match into his latest comeback, faces yet another long spell on the sidelines after sustaining the injury against Bath on Saturday.
Tuilagi completed the match but a subsequent scan showed damaged ligaments and he has now been ruled out until December.
It is a major setback for the player, club and country with England coach Eddie Jones having cleared the way for his inclusion in the squad for the autumn internationals after conciliatory talks between the two following Tuilagi’s expulsion for a late-night drinking episode during a training camp in August.
“He has to get fit, get focused, stay out of the pubs and he should be alright,” said Jones on Monday.
The only good news from another desperate bulletin for Tuilagi is that it is his left knee this time rather than the one he seriously damaged in January, keeping him out for the remainder of the season.

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As the man who destroyed the All Blacks at Twickenham in 2012 and went on to tour with the Lions the following summer, a fit Tuilagi is a force of nature.
But he has played just 17 minutes for England since Jones took charge in 2015 and has not started a Test for his country since 2014. The 26-year-old’s recent injury record for the Tigers is not much better. He has made just 17 appearances in the last three seasons.
Leicester have also been hit by a knee injury to forward Mike Fitzgerald which will rule him out for three months.