Celtic manager Ronny Deila admits his Stjarnan counterpart would have seen much to interest him after watching the Scottish champions concede five goals against Dukla Prague.
But Deila is confident his players can banish the sloppy play that led to their 5-3 friendly defeat before kicking off their Champions League campaign.
Dukla were well worth their St Mirren Park win against a strong Celtic team, bolstered by the return of nine players who were on international duty until mid-June.
But those players had only returned from their two-week summer break at the start of the week, and Israel midfielder Nir Bitton was absent because he only got back to Scotland on Wednesday.
Deila knows they will have to banish the rustiness when they play the Icelandic champions in the second qualifying round on July 15.
When asked what watching Stjarnan boss Runar Pall Sigmundsson would have made of the game, Deila said: "I think he saw some possibilities there.
"We can't play like this or we will get big problems whoever we play, if it's against Stjarnan or St Johnstone or Barcelona."
Deila, who left new right-back Saidy Janko on the bench, said: "Defensively we have good players, it's not about the quality, we just have to be sharper. We were always half a second too late. It's frustrating to watch but you just have to swallow and look forward to the next training session and match."
Deila started with Dedryck Boyata and Charlie Mulgrew in central defence, which was filled by Efe Ambrose and Virgil van Dijk after the break.
But they were behind for most of the game with midfielder Marek Hanousek helping himself to a hat-trick for the visitors, while Leigh Griffiths, Gary Mackay-Steven and van Dijk scored for Celtic.
Deila added: "It was a good test for us. They are a good team. I don't think we had a good performance but it's early. We have been back four days with 60 per cent of the team.
"Of course I want to win every game we play and have good performances but that's not how football is. You have to make yourself ready for good performances.
"You can see the players who have trained longer are sharper than the players who have only been here for one week.
"Now we have a good week of training and then Real Sociedad (in a friendly). We have no injuries, everyone is available, and that's the positive thing."
Substitute goalkeeper Leo Fasan struggled with his kicking and Deila confirmed he is still looking for another player as back-up to Craig Gordon.
The Norwegian refused to divulge any details on Celtic's pursuit of Nadir Ciftci after having two bids for the striker rejected by Dundee United.
"I can't comment on anything before we have anything ready," he said. "We have different players we work with and we'll see what we can get arranged."
And Deila revealed it was an easy decision to sell full-back Adam Matthews to Sunderland.
"One year left on his contract, a good offer, and he wanted to try something else," he said. "It was the right time to do it."
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