The 27-year-old has not played since sustaining a problem in the 3-0 FA Cup win against bitter rivals Sunderland on January 6.
Joelinton was initially told he could be out for six weeks but further tests have revealed the issue is more serious than first believed.
The Athletic report that the Brazilian midfielder needs an operation on his tendon.
On the injury, Eddie Howe said: “He’s a huge player for us, it’s a big blow.
“He’s got a problem with the tendon in his quad. It’s a very difficult place to get an injury, hence the timeframe.
“He’s very disappointed. We’ve had to do a job of picking Joe up.
“We’re really stretched in attacking and midfield areas, we have been for a long time and it’s inhibited our ability to rest players and change within games.”
Joelinton has played in 23 games this season, scoring three goals.
It has been a disaster week for him after his house was broken into by thieves.
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Newcastle have had to deal with an injury crisis for much of this season with Nick Pope, Javier Manquillo, Joe Willock, Elliot Anderson, Harvey Barnes and Matt Target all currently sidelined.
Meanwhile, Jacob Murphy, Callum Wilson and Tino Livramento are all being assessed and are nearing comebacks.
The Toon are further stretched in midfield due to Sandro Tonali serving a ten-month betting ban.
Newcastle may look to bolster the squad in the January transfer window but financial restrictions are limiting their spending.
They have been linked with a loan deal for Manchester City’s Kalvin Phillips.
However, the deal is reportedly off due to FFP rules.