The Irishman was a second half substitute against for the Hatters during the 1-0 victory but left the field of play in the 88th minute with a suspected broken leg following a heavy clash.
It has now been confirmed that the 28-year-old has fractured both his tibia and fibula and will now miss the rest of the campaign. O'Kane was transferred to Luton and Dunstable Hospital after the after the incident and will undergo surgery on Sunday.
O'Kane joined the Hatters on loan until January last month in a bid to find some competitive minutes after failing to break into the first team picture at Elland Road this season but made just three appearances for the club.
The 28-year-old signed for Leeds from Bournemouth on a two-year deal back in August 2016 and the Republic Of Ireland international was handed a new four-year contract last August.
But the midfielder then struggled for form last season and was told he would not be involved at Leeds under new head coach Marcelo Bielsa this summer which resulted in him training with the club's youngsters as a result.
The midfielder will return to Thorp Arch for his rehabilitation following his discharge from hospital.