Slovan Bratislava boss Vladimir Weiss faces a race against time to recover and see his side make their Champions League league stage bow at Celtic on Wednesday after missing two games in a row.
Celtic open their campaign as huge favourites against the Slovakian champions, who are playing in the group stages for the first time.
Slovan warmed up for the game with a last-gasp 2-1 win at Dunajska Streda thanks to a late penalty.
However, veteran boss Weiss was absent from his second game in a row after also missing their Slovakian Cup midweek victory against AC Nitra too.
And his assistant manager Boris Kitka admitted the club's manager will be assessed to see if he is fit enough to travel to Glasgow.
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He said: "Vladimir has had a pretty bad virus for the last few days, almost since the beginning of the week. We hope he will be better as soon as possible.
"For the last three to four days he was really not feeling well, he had high temperatures and the weather here is not ideal either, so he stayed at home.
"I think we controlled the game very well and I want to praise the players for the way they reacted to losing a goal.
"It's always very difficult to win here and I have to point out that the players' attitude was exemplary. We are in a good place for the challenges that await us."
And Slovan goal hero Tigran Barseghyan insisted they are confident ahead of their trip to Scotland.
The Armenian international winger said: "We are going to Celtic to try and win the game.
"When you have a strong mentality like we have in this team, you can believe anything."
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