RONNY DEILA told his players to believe as they went toe-to-toe with Inter Milan in the San Siro.

Today, as he reflects on the manner in which his side exited the Europa League, the Celtic boss retains full belief in his brave Bhoys.

However, Deila's conviction is every bit as strong that they are not progressing beyond their fourteenth game in Europe this season not because they are not good enough, but because another man on the pitch wasn't up to the task.

The performance of Slovakian referee, Ivan Kruzliak - who sent off Virgil van Dijk for two cautions and booked another five of his team-mates, while rejecting two penalty claims - led the Norwegian to pick his words carefully when asked if the match official cost them the tie.

He said: "He had a bad day at work. If we'd had that day, we would have lost five or six zero."

The cuteness of the statement ensures Deila will not be the subject of a Uefa investigation - a fate which will not escape the club after, again, some of their fans let off flares during the match.

Nevertheless, the words used conveyed the depth of disappointment felt by Deila, who truly believes his players have progressed far enough since starting out on this European journey in Reykjavik in July to have the capacity to knock out a side with the pedigree and resources of Inter.

He now hopes they can take heart from the way they competed, especially when down to 10 men, and that they have had their appetites' whetted for another crack at Europe next season.

More immediately, he needs to see clear evidence they can pick themselves up, dust themselves down and be ready to face Aberdeen on Sunday.

John Beaton is in charge at Parkhead, and Deila can only hope the Scottish official is not as overawed by the occasion as Kruzliak appeared to be in the San Siro.

The Hoops boss reckons Van Dijk's dismissal was 'very cheap', but admired the way those left on the field regrouped and held out almost to the end.

He said: "It was a very disappointed gang of players who came into the dressing room. I felt very sorry for them, but I'm very proud of them. We had a very good performance for 90 minutes.

"When it was 11 v 11, we had control of the game and had one very big chance (Gary Mackay-Steven through on goal, but his shot was saved). When we had 10 men, we defended very well, but we could not create anything.

"So, it's tough. But this just needs to give us motivation to get back on this stage. We showed we have something more to do on this level.

"We have to use that in our domestic game to get back out into Europe, and, hopefully, in the Champions League."

He added: "I think there was a very good chance to go through. Inter are a good team, so we have to get over it and start focusing on what is going to happen on Sunday."

When analysing what occurred, and what might have been, in the San Siro, Deila will also dissect his own performance, especially the team selection and changes made during the tie.

The decision to remove Mackay-Steven to allow Efe Ambrose to fill the gap left by Van Dijk's red card was met with relief by Inter, who had been wary of the threat he carried as he ran at them.

Losing Leigh Griffiths to injury a matter of hours before the tie helped Deila's dilemma as telling John Guidetti he was starting on the bench after his stoppage-time heroics in the first leg would have been a tough call.

Leaving Kris Commons there until 12 minutes from time was another huge call, especially as Celtic always knew they had to score to go through.

Ultimately, that proved beyond them.