A furious Neil Lennon said he is sick of the number of chances his side are squandering after they slumped to a shock 1-0 defeat at home to St Johnstone on Sunday.
The Celtic manager watched as Kris Commons had his second-minute penalty saved before his side missed a host of chances to take the lead against the visitors from Perth.
Celtic were made to rue their wastefulness in front of goal on the hour mark when Dave MacKay's volley deflected off Joe Ledley and past Fraser Forster for St Johnstone's first goal of the season.
Despite laying siege to the St Johnstone goal in search of an equaliser the Saints defence held firm to record their first win at Parkhead since 1999.
Celtic had a host of players missing for the match due to injury but Lennon was angry at the men who came in for failing to take advantage of their opportunity to shine.
"We should do better. We had all the game really and we were immature - that is one word to describe our performance," the Hoops boss said.
"I am fed up with us missing penalties as it would have given us a real good start.
"I am really angry as we threw it away. We missed clear-cut chances in front of goal and we were wasteful. We keep missing simple chances and I am fed up with it.
"Our general play was alright but in the final third again we were awful.
"My front six were bang average to say the least so I am more angry at them than anyone else.
"Maybe we didn't deserve the result but we've got it and if you don't take your chances then that's what happens in football.
"My point is that there are players out and the players who come in have got an opportunity to make a stake for the team. They didn't do that and they failed."
The performance came on the back of Thursday's goalless draw in their Europa League play-off tie against Sion.
Celtic go to Switzerland for the return leg this coming midweek and Lennon says he is looking for a big improvement from his players.
"We have a big game on Thursday. We have had a poor result and a poor performance going into that game so there's no better way to turn things round than to go and play a positive game on Thursday night," the Northern Irishman said.
"I'm looking for a huge reaction from everybody. They need to toughen up a bit mentally in terms of the quality of their play, in terms of them seeing out games and all the mature things you expect from a team that's going for the title.
"The way we didn't handle the crowd after they scored was a concern for me as well.
"There was a bit of panic set in. I understand the crowd's frustration but the players have to handle that situation a lot better.
"However it is only four games into the season and I'm certainly not panicking and I know we will get better from that."
Old Firm rivals Rangers seized top spot, and moved one point clear of third-placed Celtic at the top of the Scottish Premier League, following a 3-0 away win over previous leaders Motherwell.
Steven Naismith, Kyle Lafferty and Gregg Wylde got the goals for an injury-ravaged Rangers, who made five changes to the side that lost in the Europa League to Maribor as Ross Perry and Jordan McMillan were handed their first SPL starts.
"We have to nurture our younger players," Rangers manager Ally McCoist said.
"We can't get carried away, it's one game, that's all it is, but it's a step in the right direction for some of the younger boys."
Source: AFP
