Ronny Deila's dejection at exiting the Europa League was tempered by pride in his Celtic players as they ran Inter Milan close in the
The Celtic manager was unhappy at the first-half red card shown to Virgil van Dijk and felt Slovakian referee Ivan Kruzliak "had a bad day at work".
"It's a very disappointed gang of players in the dressing room," said the Norwegian after the 4-3 aggregate loss.
"I feel very sorry for them but I'm very proud of them."
Craig Gordon was in superb form in the visitors' goal as he produced a series of saves to deny Inter, who Deila believes are good enough to win the tournament now they are through to the last 16.
Yet it was Celtic winger Gary Mackay-Steven who had the first attempt on target, as early as the sixth minute, when he shot straight at Inter keeper Juan Pablo Carrizo.
In a high-tempo opening half hour, the teams looked as evenly matched as the first-leg 3-3 scoreline suggested but the nature of the contest changed when Dutch centre-half Van Dijk was shown two yellow cards for two challenges, the first of which looked soft.
"We gave a very good performance for 90 minutes. I think we showed we can do something at this level," said Deila.
"When we were 11 against 11 I think we controlled the game. We had one big chance. It's tough but I'm proud of how the boys performed.
"I think it was a very good chance to go through today. I felt it the whole day.
"It gives us motivation to get back on this stage. We have to use that domestically so we can get back in to Europe, and hopefully the Champions League."
Asked about the referee's performance, Deila answered: "He had a bad day at work. If we had that day we would have lost 5-0 or 6-0.
"The sending off made it very difficult for us and we had to work really hard in defence.
"We wanted to go not so much with the full-backs like we normally do. We were not so offensive with the full-backs but I think defensively we did a good job.
"We hoped to keep it for a long time and get a chance in the end but we didn't make it.
"Inter is a good team. We just have to get over it and focus on what is going to happen on Sunday."
On Wednesday Celtic were fined £7,300 by Uefa for their fans letting off flares at the Europa League away match against Dinamo Zagreb in December.
Celtic may incur further Uefa sanctions as some of their supporters also discharged flares in the stadium in Milan.
"That's very disappointing, of course," said Deila.
"We have to get rid of this. This has nothing to do with football. The fans were unbelievable again today but we have to behave in the right way."