Celtic manager Neil Lennon says his squad players failed to take their chance to shine after the champions' much-changed side was defeated 3-1 by Motherwell at Fir Park on Sunday.
After clinching their second successive Scottish Premier League championship last weekend Celtic made six changes as they afforded several top team stars a break.
The Hoops seemed to be coping well with the changes when they took a 40th-minute lead through Gary Hooper.
However, Motherwell were level seconds before the break when Henrik Ojamaa rifled a low shot beyond Fraser Forster.
The Estonian striker then earned his side a 50th-minute penalty which Michael Higdon smashed past the keeper.
A bizarre own goal moved Motherwell further in front five minutes later when Hoops defender Mikel Lustig's header hit the back of Forster after rebounding off the base of the post.
Celtic face Hibernian in next month's Scottish Cup final but Lennon said he hadn't seen anything from his fringe players that would see them grab a place in his plans.
"It's not about today or even next week, it's about the cup final and it's about the close season and getting the players the right rest now," the Celtic manager said.
"Four were away this week and five will be away from tomorrow. It's just the way it is.
"We start back the third week in June and start playing the second week in July so it's a very heavy schedule for players and we need to get the preparations right.
"We've won the league and we will have everyone back for two weeks preparation for the cup final and you need to bite the bullet for a couple of games.
"But I still want the team to be competitive. Some players are aware that there is cup final places up for grabs but I'm not too sure they took the opportunity today.
"A few of them looked as if they had switched off in the second half which is unacceptable from our point of view.
"Goals change games and decisions change games. I think harsh decisions have gone against us however we need to do better.
"Squad players who are coming in need to really show they want to be a part of this club for the next two or three years and they need to realise what it means."
Despite his disappointment at the defeat Lennon did single out Australian international Tom Rogic for praise.
The January signing from A-League side Central Coast Mariners impressed in a rare start and Lennon was hopeful there would be more to come from the attacking midfielder.
"It would have done Rogic the world of good today. I thought he was excellent first half though he faded a little bit latterly," the Celtic manager said
"I think he's a bit short in terms of fitness levels which is understandable but once he gets a good pre-season under his belt he should be good to go next year."
Victory earned Motherwell back-to-back wins over Celtic for the first time in 14 years and moves them nine points clear of third-placed Inverness Caledonian Thistle with three games remaining.
It means the Fir Park side, who sit on 60 points, are guaranteed one of the SPL's two Europa League qualifying spots next season.
Motherwell manager Stuart McCall was proud of his side, who are on course to surpass their best-ever SPL points tally of 62, which they set last season.
"I said to the players to enjoy the moment. To play as well as that against Celtic is outstanding," a delighted McCall said.
"It's a really proud moment and I thought we won in style. I can't speak highly enough of the group of players that we've got."