The champions boast a five-point lead going into this weekend's fixtures but that will be down to two by the time they travel to in-form Aberdeen on Sunday if their arch-rivals beat Falkirk tomorrow.

With two more Old Firm derbies to play, Scotland midfielder Hartley knows Celtic can take nothing for granted.

The 32-year-old told STV: "Rangers will push us all the way. We've still got to play them twice more.

"We know it's going to be difficult but we have to make sure we're ready for it."

One player itching to play his part in the second half of the season is Jan Vennegoor of Hesselink, who claims he loves being back on the pitch so much, he has even considered eating the grass.

The Holland striker made his first start for more than two months in Saturday's Homecoming Scottish Cup win over Dundee after being sidelined by a torn adductor muscle.

Vennegoor of Hesselink, 30, had initially been expected to make a swift recovery from the injury suffered inside the opening seconds of the October 4 clash with Hamilton.

But the problem proved far more troublesome than first thought and he was out of action until coming off the bench in last month's Old Firm derby win at Ibrox.

He told Celtic TV: "Normally, if you have a few small injuries it is not bad. But now it is one big one which kept me out for almost two and a half months.

"It's a shame you can't play, especially in the busy time from October to December when you have vital games in the Champions League and the SPL.

"You want to be involved in these. If you can't, then you are a little bit frustrated because you are looking at it from the side when you want to participate.

"But these are the things you have to deal with and now I'm fresh again and almost want to eat the grass and play football again."

Vennegoor of Hesselink will now vie with Georgios Samaras and Scott McDonald for a starting berth.

He said: "It doesn't matter who plays. Sometimes you sit on the bench and hope to come on and make a little bit of a difference.

"Competition is something you have to cope with as a footballer. It makes you stronger and keeps you on your toes.

"I hope I can give Scott and Georgios competition so that we can make it a difficult choice for the gaffer and also improve the team again."

Meanwhile, Dons boss Jimmy Calderwood has urged the club's fans to fill Pittodrie for their upcoming Old Firm double-header.

Aberdeen host Rangers next Saturday, six days after welcoming Celtic.

Calderwood told the Evening Express: "We need the Aberdeen fans big time in the games against the Old Firm. They can make a huge difference by getting right behind the team and cheering them on.

"Hopefully, they will pack out Pittodrie and create a great atmosphere.

"Aberdeen's fans did it against Hearts - their support was important.

"In many ways it reminded me of the European nights against Bayern Munich and FC Copenhagen last season.

"It gives the players a lift and hopefully it will be the same against the Old Firm.

"Sunday's game against Celtic is massive and if the fans turn up like they did against Hearts I am sure Pittodrie will be buzzing."