The coach has been discussing the Manchester City loanee.
The Manchester City striker has been in impressive form since joining Celtic on loan but Deila says he reflects a little too much on what he has done wrong after a match.
And the Manchester City loanee needs to see more of the positives in his game, according to the Norwegian.
“I think John’s spirits are too high,” the Celtic boss is quoted as saying by the Scotsman. “That’s the problem. He needs to calm down. He does a lot of thinking but you can’t do anything about results unless you do something about the process and the performance.
“It’s about the next move, instead of thinking ‘I have to score’ or ‘I have to win’. He is very up about scoring goals and you can see his frustrations.
“But I also see positive things. John could have had four assists in the first half and got one, a great touch and pass for James Forrest to score. Sure, he missed chances but so did Stefan Scepovic when he came on and Stefan Johansen also missed three or four."
Celtic are reportedly interested in taking Guidetti on full-time but it remains to be seen whether he will leave Manchester City.