Leeds will be without hooker Paul Aiton for the next three months as he undergoes a course of treatment for a medical condition.
The 28-year-old Papua New Guinea international played in the opening six matches of the 2014 First Utility Super League after making the move to Headingley from Wakefield but has been forced him to sit out the Rhinos' last two games.
Leeds chief executive Gary Hetherington said: "Paul is desperately disappointed because he feels fit and healthy but, after tests and consultation with a specialist, he has been advised that he needs a course of medication.
"He will not be able to play whilst taking this medication until he has made a full recovery. This process is expected to be about 12 weeks, but he will be monitored on a monthly basis."
Aiton said: "I'm so enjoying being part of the Rhinos team and really disappointed I will be out for so long. But I'll do all I have to and be back raring to go."
The loss of Aiton is the second major blow to hit the Rhinos in a week after England second row forward Jamie Jones-Buchanan was ruled out for up to three months with a torn bicep.
It is likely to mean an extended run at hooker for Rob Burrow, who has been sharing the role with Aiton this season.
Leeds coach Brian McDermott said: "Paul had settled in really well so to be losing him and Jamie Jones-Buchanan for the next three months is a blow but at least they'll both come back at a crucial time of the season pretty fresh and fit."
Meanwhile, Leeds have confirmed that their glamour Tetley's Challenge Cup fifth-round tie against St Helens will be played at Headingley on Saturday, April 26, with a 2.3 0pm kick-off.
Promotion-chasing Leeds Carnegie, who share the Headingley stadium with the Rhinos, agreed to bring forward their final home Championship match of the season against Cornish Pirates to Friday, April 25, to enable the televised cup tie to go ahead.
Carnegie chairman Sir Ian McGeechan said: "Obviously this is a huge game for the Rhinos and the stadium with it being televised live on the BBC. When we received the request we were happy to work with the RFU and Cornish Pirates to move our fixture and hopefully it will make for a great weekend of rugby at Headingley Carnegie."