Ronny Deila says it was hard to take after his hopes of leading Celtic to a historic treble in his first season in charge of the Glasgow giants were extinguished by a 3-2 defeat to Inverness Caledonian Thistle in their Scottish Cup semi-final.

The Norwegian had been hoping to become just the third manager in the club’s 127-year history to claim a clean sweep of domestic trophies, a feat last achieved by Martin O’Neill in 2001.

The Hoops arrived at Hampden with the League Cup already in the trophy cabinet and a five-point lead at the top of the Scottish Premiership as they chase a fourth successive title.

However, their semi-final fixture was marred by controversy when Deila’s side were denied a penalty on the stroke of half-time when Josh Meekings stopped a Leigh Griffiths header with his arm, which would have given them a chance to build on Virgil van Dijk’s 18th minute opener.

Despite the presence of an extra official behind the goal the incident was missed, something that rankled with Deila.

“It has been a tough day and it was hard to take,” he said.

“I don’t think I have to say much about the penalty incident. I think everybody saw what happened.

“Maybe we need seven referees? One on each post? Their one task is to look at what is happening in the six-yard box and on the goal line. You can’t blame the main referee for that, but this mistake was very hard to take.

“It’s a hard blow for the boys and for us. We’re very disappointed and we had control when it was 11 versus 11 and we should have killed the game off.

“Everybody of course was angry about it.

“It’s small details that can make you fail and today it was a small detail that made it hard for us. That’s why it’s so hard to get a treble.”

The Hoops, who are back in league action away to Dundee on Wednesday, are just four wins from claiming the title and Deila said it was important his side now focus on that.

“Good teams bounce back quickly. On Wednesday we have to be back on track again and that is what we are aiming for,” he added.

“Everybody is very disappointed today (Sunday), but I’ve had disappointing moments before in football. It’s how you handle it and what you learn from it that’s important.

“We still have a lot to fight for. We’ve done a lot of good things so far and if we win the league as well then we’ve had a good season.”

It will be a first appearance in the Scottish Cup final for Inverness, who will face Falkirk on May 30 after the Bairns defeated Hibernian 1-0 in Saturday’s semi-final.

Greg Tansey had levelled from the spot for Inverness after Celtic keeper Craig Gordon was sent off for hauling down Marley Watkins. Edward Ofere fired Inverness in front in extra time before substitute John Guidetti equalised.

With time running out, David Raven blasted home a winner in the 117th minute to seal a famous victory for Inverness, to emulate their side of 2000 who knocked Celtic out of the same competition while they were First Division part-timers.

“There are a lot of heroes in there. It is an absolutely fantastic story. We have been going 21 years and are a small provincial club up there in the Highlands,” Inverness manager John Hughes said.

“I didn’t realise it is the first time the club has been in the final of the Scottish Cup, so it is a remarkable achievement.”