Ronny Deila has described Celtic's Scottish Cup semi-final against Inverness Caledonian Thistle on Sunday afternoon as the biggest game of the season for the Parkhead side.

The Norwegian has been candid throughout the campaign about his quest to claim a domestic Treble in his inaugural season in charge of the club.

It has been a bold declaration and as the season nears to a close that which was blurry and indefinite is drawing into sharp focus; the opportunity for Celtic to realise that ambition is tantalisingly close.

Yet, if there is anything that may lend Celtic a sense of perspective ahead of Sunday's meeting, it is their form in the domestic cups in recent seasons.

Last season Morton and Aberdeen halted the Hoops in the League Cup and Scottish Cup respectively, while the year before that St Mirren stunned Celtic in the League Cup semi-final with a 3-2 win at Hampden.

Inverness did well to frustrate Celtic last weekend when the teams met in the Highlands on league duty. And Deila believes that in order for the Hoops to progress to the final of the Scottish Cup they will need to start the game at Hampden in the same way they finished it at Celtic Park on Wednesday night.

For an hour Deila's side toiled to open up at resolute Killie defence before Leigh Griffiths came off the bench to cause havoc and the Hoops boss wants to see his side play at the same tempo as they did in the latter stages of that convincing win.

"This is the biggest game of the season for us now," said Deila. "It is so important. It has been an important week and this is the biggest game of them all now. We know how big a game it is and what it can lead to for us. We need to win.

"We want to win the Treble. We have been saying that since we started playing in August. We are now getting to the end of the season and the chance is there for us to go and achieve that. But there is so much hard work for us still to do.

"Inverness are a very good team. They will make it difficult for us because they want the prize the same way that we do. We need to keep the play moving at a good tempo. Although we were strong defensively against Kilmarnock, the passing was not fast enough The movement was not enough.

"You saw in the second-half that the ball was moved around quicker that we got more players in behind them and the goals came - but so did the chances. We want to start the game on Sunday at that level."

John Hughes was open about his optimism that Celtic being in action midweek could play into the hands of Inverness who have had extra time to prepare for the Cup clash at the national stadium.

While that may have worked more in his favour had Celtic dropped points, the fact that the Parkhead side enjoyed such a convincing win in actual fact may work the opposite way for the Highland outfit who will now face a Celtic side who are full of confidence and belief.

If this current Celtic team are to write their names into the record books and become only the fourth team in the 127-year history of the club to win a Treble then this game against Inverness will be definitive in the journey.

And Deila does not believe that the 90 minutes against Killie will have any bearing on what goes on at the national stadium on Sunday.

"The thing is that we love playing football," said Deila. "We like to play games. We love to win.

"The confidence in the team is good and there is a good spirit among the players. So I can't think that there would be anything negative for us from playing a game this week.

"Our game against Inverness is on Sunday which means that we have an extra day to recover - having four days instead of three is always much better and gives you the best chance of recovery.

"Whatever happens on Sunday will not have anything to do with us playing on Wednesday night."

Meanwhile, Deila has conceded that Mikael Lustig is unlikely to feature for the club between now and the end of the season.

The Swedish defender has been out of action since February with an ankle problem that stems from ligament damage and bruising on the bone. It is the bruising on the bone that has caused the problem and although no surgery was required, the injury required a three-month rehabilitation.

And Deila would like to have Lustig fully fit and available for pre-season training this summer.

Charlie Mulgrew, however, could rejoin training this week although he is another that will not be reintroduced to the fray too early.

"It would silly of us to gamble on Mikael or Charlie," said Deila. "We won't risk Mikael coming back too quickly because he has been out for a long time. The bruising has been difficult to assess.

"We would like to think he might have a chance of being back before the season finished but we won't throw him in just for the sake of it.

"The same goes for Charlie. He is further ahead and is expected to join training with us next week so hopefully he will get some games before the end of the season.

"They are two important players for us so we want them to come back but we want them to come back strong rather than coming back and picking up more injuries. The timing has to be right."