The Celtic players were put through their paces at Lennoxtown on Tuesday as they gear up for the biggest match of the season so far.
Ange Postecoglou's men have cut the gap at the top of the Premiership to just two points, and know they'll leapfrog Rangers with a win on Wednesday night.
A packed Parkhead will be craving a result as incredibly it's over two years since Celtic have got the better of their Glasgow rivals.
As a result Postecoglou will have been looking out for any signs of slackness in training with a massive match on the horizon.
Here are five things we spotted at Lennoxtown.
McCarthy stakes his claim
Celtic are hoping to have Callum McGregor back for the big one, with the skipper able to train wearing a mask following his horror injury against Alloa.
With Nir Bitton suspended and Yosuke Ideguchi working his way back from injury the captain being back would give his manager another option in a deep midfield role.
Postecoglou was keeping his cards close to his chest ahead of the match, but there is at least a chance that the Scotland star will miss out.
In that case summer signing James McCarthy could be given the nod in the engine room.
It's fair to say the 31-year-old's Celtic career hasn't really got going yet, with the midfielder making just four Premiership starts and completing the 90 minutes only twice.
McCarthy has managed a grand total of 11 minutes since the winter break but was certainly in the thick of it at Lennoxtown - is this his chance to really make his mark?
Dembele on the way back
Once seen as a future star, Karamoko Dembele has had a hard time of it this season.
The diminutive winger picked up an injury in pre-season and is yet to make an appearance under Postecoglou.
The 18-year-old was in training ahead of the Rangers match though as he prepares to make his long-awaited return.
The derby will surely come too son for him but fans will be delighted to see a top prospect on the way back.
No pressure for Welsh
If the atmosphere was tense before the biggest game of the season so far, centre-back Stephen Welsh certainly wasn't showing it.
The Scotland international could be seen laughing and joking as he appealed for a training ground decision.
The big centre-back was a target for Udinese in the window but Celtic made clear there was no chance they'd be letting him move to Serie A.
Welsh was thrown in against Rangers last season in difficult circumstances and will be itching to get his chance tomorrow.
Youngster gets a taste
There was an unfamiliar face at Lennoxtown as young goalkeeper Tobi Oluwayemi was once again called to work with the first team.
The former Tottenham youth worked alongside Joe Hart, Scott Bain and Vasilis Barkas and has been given his chance with the seniors after the recommendation of coach Stevie Woods.
He's likely to be in the Europa League squad after Conor Hazard's loan move, and has already been talked up by Postecoglou.
He said: "Tobi’s an exciting young goalkeeper. He was playing with the B team, but I feel like it’s time we expose him to our first-team environment, particularly at training.
“He’s a pretty lucky young man because he’s got an ex-England No1 and a guy who has reached the very top as a goalkeeper training with him every day. It’s going to be priceless.
"I didn’t want to waste that opportunity, so he’ll be training with us regularly and, hopefully, we’ll watch him develop over the next couple of years.”
A familiar face still around
It was a successful window for Celtic in terms of incomings but they failed to get a number of fringe players off the books.
Albian Ajeti and Vasilis Barkas remain at the club, with the Greek goalkeeper training at Lennoxtown on Tuesday.
And another one who is proving hard to shift is left-back Boli Bolingoli.
He's barely been seen since his ill-advised trip to Spain 18 months ago, making just two appearances this season.
He hasn't played since a win over Motherwell in October but was unable to agree a move away in the window.
With another 18 months remaining on his contract, Celtic fans will hope he doesn't turn into another Cristian Gamboa or Eboue Kouassi.
