That would rule him out of Wednesday’s cinch Premiership trip to Ibrox and Sunday’s Scottish Cup fifth round tie at Gayfield against Championship leaders Arbroath.
The home match against Ross County on February 19 could be the target date for his potential return.
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Newell limped off in the Edinburgh derby against Hearts in the 69th minute and was replaced by Josh Campbell. He was an unused sub in the previous match against Livingston.
Before then was a regular in the centre of midfield under Jack Ross and Shaun Maloney, making 27 appearances this season altogether and captaining the team at St Mirren in December.
With Kyle Magennis still unavailable for selection and still some way off being ready to return from his own long-term injury, Newell’s absence would reduce the central midfield option available Maloney ahead of two difficult but very different matches this week.
Jake Doyle-Hayes and Josh Campbell started against St Mirren, while Ewan Henderson came on at half time in a more advanced central midfield role.
Popular playmaker Scott Allan is another option. He started Maloney’s first game in charge on December 22 – the 1-0 home win over Aberdeen.
But Alex Gogic and Melker Hellberg were both offloaded during the January transfer window.
There are more defensive options available for the trip to Ibrox, with Paul McGinn back amongst the substitutes against St Mirren after missing the derby.
Paul Hanlon will be assessed ahead of the trip to Ibrox, but new signing Harry Clarke remains out of the equation.