Leigh Griffiths: Celtic striker should relish challenge of Patryk Klimala - John Hartson
Celtic striker Leigh Griffiths should see the arrival of Patryk Klimala as "a challenge", says former Parkhead forward John Hartson.
Poland Under-21 cap Klimala joined Celtic from Jagiellonia Bialystok on Tuesday for a reported £3.5m.
Scotland international Griffiths has started only one game since recovering from a thigh injury in November.
"If you're Leigh Griffiths, you see it as a challenge," Hartson told BBC Radio Scotland's Sportsound.
"You want to stay and prove you can still do it at this level. He's been pivotal to Celtic's success in recent years."
Griffiths, 29, took time away from football last season to address his mental health and has been unable to displace first-choice Odsonne Edouard in Neil Lennon's line-up since regaining fitness.
Lennon has also deployed highly-rated 20-year-old Mikey Johnston in the striker's role, with Vakoun Issouf Bayo making 12 appearances this term, albeit only two were starts.
Earlier this week, Griffiths deleted his Twitter account after posting an image from Celtic's Christmas video in which he has his fingers in his ears, fuelling speculation over his future.
"Leigh is a goalscorer," Hartson added. "It will be interesting to see whether there are whispers that he's really not happy, wants to move, wants more game time, or can Neil persuade him and say there are still opportunities and he still has a major part to play?
"When you've got too many players fighting for a certain position, you are going to get one or two unhappy. That's when the manager is very important by still keeping them hungry and when they do get that chance, they make sure they are ready."
Hartson would like to see Celtic continue to bolster their squad in the January window as they bid to win a ninth-successive Scottish top-flight title.
Lennon's side top the standings but are just two points ahead of Rangers, who won last month's Old Firm derby and have a game in hand.
Celtic return from their warm-weather winter training camp in Dubai with a Scottish Cup fourth-round trip to Partick Thistle on Saturday, before their Premiership campaign resumes with a visit to Kilmarnock four days later.
"Klimala is unknown. He looks quick, but I'd be lying if I said he's fantastic," Hartson said. "It's a great opportunity for him, but I still feel they need a couple more.
"They're certainly not walking this league. Most fans have had a wake-up call, they're wanting Celtic to come back from Dubai refreshed, hungry and realise what's at stake may never happen in these players' careers again."