Ronny Deila will look to lead Celtic to success in four competitions this season, but he will aim for success by using what he believes to be an effective squad-rotation system.

The Hoops boss is wary of making too many changes - he cites three or four as the most he will make for one game - but he does expect that, for Celtic to be successful, players will need to be refreshed.

And, like many before him, he has pondered whether or not there may be too many games in the domestic calendar to get the best out of his squad.

"The football is much quicker now," he said. "There are more injuries and the body gets more tired after every game because the intensity is so high.

"That's what makes it harder for players to do it every week. There can be seasons when you get lucky with injuries, but I think it is harder these days.

"You must have at least 20 players at a high level. When you consider the international matches as well, it's too many. They are playing 65 matches every year.

"I think the players love it but to get improvement all the time they need to be fresh.

"If we want people to watch, we need to have players at the best level they can be and for that they need to be refreshed and ready. Keeping the top level for 10 months, playing three times a week all the time is very hard."

The Celtic boss, though, is wary of wholesale changes that interrupt his team's fluency.

"In the past when we've made more than four changes, we have had bad results," he said.

"It happened at Inverness when we changed 10 and against Motherwell at home, when we had six or seven changes. But when we have changed three or four, we have done well every time."

That could mean that Deila will rest keys players for Celtic's final Europa League group game against Dinamo Zagreb next Thursday.

"We'll see," he said. "I haven't decided yet. It is a possibility, especially if they are struggling with some injuries. It could give them time to get two or three days off and recover for the following Sunday.

"We will have to look at all of the players individually and work out how to get them at the highest level.

"We know which players can handle playing so many games - players like Scott Brown, Virgil van Dijk, Craig Gordon and Stefan Johansen are keeping up their level and Efe Ambrose was fantastic this week.

"These players are keeping up a high level."