The 21-year-old, who has been earmarked for a place in England coach Shaun Wane’s World Cup squad at the end of the season, has been out since last September but had been expected to return against St Helens in a fortnight’s time.
However, Rhinos coach Richard Agar said the target date has been put back at least six weeks after scans showed his leg has not sufficiently healed.
Agar said: “He had a scan this week and he still has got some more healing to do, which is frustrating for him.
“We were all systems go but it’s such an injury that, if it’s not healed properly and it goes again, then we have major problems.
“It’s not like it wasn’t a major problem anyway but I’m talking major, major problems that could put a question mark on his career.
“It healed really well really quickly and it’s just tapered off a bit. So he’s had a bit of a setback and some disappointment but it’s not that there are any complications with the injury.
“His next scan is in six weeks’ time so we’ll have to wait another six weeks rather than three at this moment but we accept that.
“It’s such a big, traumatic injury. It’s disappointing in the short term but we’ve said all along it’s about the bigger picture.
“He’s such a brilliant talent with so much of his career in front of him.”
With Newman’s replacement, Alex Sutcliffe, also sidelined through injury, winger Tom Briscoe is currently filling in at centre and Agar says he will resist the temptation to make changes for Friday’s Super League derby against Castleford at the Mend-A-Hose Jungle.
Defeat by Hull last Sunday means Leeds have taken just four points from their opening seven matches but the coach is refusing to panic.
Agar added: “We still think we’re doing plenty of things right. We don’t think we have much to fix up.”