Tosun, 28, sustained the injury in training earlier this week, and according to Turkish media outlet TRT, as cited by Sport Witness, scans have since detected ruptures which could keep him out of action for as long as half a year.
It means Tosun, who has scored once in five Eagles outings since his January loan move, has surely played his last game of this season, and will also likely miss the European Championships this summer.
It will also make Everton’s task of shifting Tosun on a permanent basis this summer far harder; Palace had the option to buy the striker for a reported £20 million but this injury may well have scuppered any plans to do so.
Tosun joined Everton from Besiktas in his native Turkey for £27 million in January 2018, but has found goals in England far harder to come by, netting only ten in 51 appearances in a royal blue shirt.
He left Goodison Park temporarily in January in search of first team football, having not played a minute for Everton since Carlo Ancelotti’s appointment as manager in late December.
But this knee injury looks to have put paid to any hopes of earning a permanent move to Selhurst Park, or adding to his only goal in an Eagles shirt so far, a header in a 2-2 draw at Manchester City in January.