Leigh Griffiths has four weeks to save his Celtic career, according to ex-Rangers striker Kris Boyd.

Griffiths stepped off the bench this afternoon in his side's 4-1 win over Ross County.

He continued his return to fitness with another cameo on Thursday evening against Rennes in the Europa League.

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The Scotland cap has not scored since August when he netted a free-kick against Motherwell.

And Boyd believes manager Neil Lennon will dip his toe into the transfer market in January for another striker if Griffiths, 29, doesn't show he deserves to be at the front of the queue in Odsonne Edouard and Vakoun Bayo's absence.

"I think the days of playing games to get your fitness levels up are done in football," Boyd told Sky Sports.

"You need to be doing it in training, you need to be doing it day in, day out.

"That's why players are at the top of their game now.

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"You look back at yourself and think you have done a bit more in training some days? Maybe you could have.

"Leigh Griffiths right now is at that crossroads in his career.

"He needs to be first in, he needs to be last away. He needs to train every single day to the best of his ability because he's not going to play.

"He's miles behind Odsonne Edouard.

"For me, he has got four weeks to save his Celtic career.

"If he doesn't show Neil Lennon inside these four weeks, they will go and recruit a striker in January and for me, it will be over for Griffiths."