The Romanian international playmaker suffered the damage in the early stages of the Scottish Cup fourth round tie against Stirling Albion at Ibrox last Friday night, limping off to be replaced by debutant Alex Lowry.
Rangers manager Giovanni van Bronckhorst has revealed that Hagi had to undergo surgery on Monday and is now facing a lengthy lay-off.
“Sadly we will be missing Ianis for the season,” said van Bronckhorst. “I spoke to Ianis yesterday, he is positive and focused on his recovery.”
Hagi, who initially joined Rangers on loan from Belgian club Genk two years ago before making the move permanent in a £3 million deal, has been a significant success in Glasgow.
The 23-year-old has scored 15 goals in 86 appearances and contributed more assists than any other player in Rangers’ title-winning campaign last season.
There is some better news for van Bronckhorst with midfielders Ryan Jack and Scott Arfield both back in full training and included in his squad for Wednesday night’s Premiership fixture against Livingston at Ibrox.
Steven Davis will still be missing, although he is expected to return to training soon, as will Joe Aribo who is due to return to Glasgow on Tuesday night following Nigeria’s exit from the Africa Cup of Nations finals in Cameroon.
Van Bronckhorst indicated that Aribo will be back in the Rangers side for the trip to face Ross County in Dingwall on Saturday.