Brendan Rodgers has revealed Kristoffer Ajer is a big doubt for Celtic's Europa League group B opener against Rosenborg, with the 20-year-old struggling with a virus.
Fellow defender Jozo Simunovic is also sidelined with a knee injury, but Rodgers insists he is excited for European football ahead of Thursday's clash.
The Hoops knocked the Norwegian outfit out of the Champions League qualifiers last month, but they failed to reach the group stages as they then lost to AEK Athens.
The Celtic manager said: "There is always excitement going into the European competitions and this is no different. It is a real good group we are in.
"The dynamics are slightly different in terms of playing Rosenborg, previously it has been knockout and maybe the first legs have been a little bit cagey. But the difficulty of the game is still there."
Rodgers added: "Rosenborg come into the game in really good form since we last played.
"We expect a tough game. We are playing at home and like any other games against them we really want to show our quality.
"It is always a challenge and it doesn't matter how many times you play an opponent.
"We prepare well. They are a good team. We respect their qualities but we want to bring our game, our energy and quality and hopefully look to start the group with three points."