Brendan Rodgers has laid down the gauntlet to two fringe players who stuttered against Dundee United.
The Celtic manager made four changes to his side against the Tangerines and allowed squad players to come in and attempt to upset the apple cart.
South Korean winger Yang started on the wing in the place of the injured Nicolas Kuhn who still does not have a return date.
The wide man, 22, had moments on the Tannadice pitch but he failed to really cause too many issues for the hosts.
Another who struggled was Luis Palma who has MLS January transfer interest in his services.
The Honduran was predictable in his attacks and Palma was criticised by Pat Bonner at full-time of the action last weekend.
Manager Rodgers was not particularly happy, either, with the pair and he explained how they will both have to improve significantly to ensure they still have a chance of cutting it in Glasgow.
Luis Palma and Yang Hyun-jun have been challenged by Rodgers
Rotation will be key for Rodgers and Celtic as the boss has so often proved.
And with the transfer window officially open next week, he will have other possible signing options.
Until then, however, he has challenged those who are already in the building to do more and show why they deserve the opportunity to stay and fight for their spot.
And he hopes they can do just that.
What Brendan Rodgers said about Celtic’s fringe players struggling
“You need to come in and hit the ground running,” Rodgers insisted.
“They have been out of the picture for a long time but they train to a level and they come in and do their best.
“They work every day to allow them to be physically good and then you are just looking for that bit of magic from one of them that can unlock a defence.
“Luis had a good shot and I thought it was going into the bottom corner until the centre-half got a block on it but that’s the possibility for these guys.
“We have so many games and we will need everyone to contribute.
