Guidetti out, Griffiths in hints Celtic boss Deila
Guidetti, who is on loan at Celtic from Manchester City this season, has not hit the back of the net in the league since last month and again fired blanks in his team's 2-1 loss at Dundee United on Sunday.
Instead, Leigh Griffiths got on the scoresheet for Deila's side, scoring just his second goal of the season after coming on for the final 12 minutes.
Injuries have meant Guidetti - who has played just five senior games for City - has barely played since he was on loan at Feyenoord in the 2011-12 season and Deila reckons it is understandable the 22-year-old Swede is suffering a "little dip" in form.
"There is one thing you have to remember with John Guidetti: he hadn't played football for two years before he came here," Deila said.
"He started very well and now he has had a little dip. That is because he has to be physically stronger and play matches over time.
"All strikers go through periods like this. But again we have to focus on what is going to get him out of this situation.
"For me, it's to be even more concentrated in training and in matches and everything you do. That will come."
Deila hinted that Celtic may need to use other options up front during the busy Christmas period.
Celtic will host Ross County on Saturday in their first of three matches in 10 days in the Premiership.
"We have to pick the team we think is the best for every game," the Norwegian manager said.
Griffiths, who has only started one match in the league this term, had not seen action for four straight matches for Sunday's clash with Dundee United but has impressed the former Hibernian striker's work-rate in training.
"He has been working well to get into better shape and he is now," Deila said.
"He scored two goals against Sunderland on Thursday [for the development squad] and he's scored today as well.
"That's the way to do it, show it by playing football that you can score goals."
Guidetti has scored six goals in 13 Premiership fixtures this season, helping Celtic to a four-point lead over Dundee United and Aberdeen at the top of the table.