Gary Hooper and James Forrest are already rated doubtful to be fit for a match which could seal the Hoops' passage to the last 16.
Manager Neil Lennon (left) acknowledges it would be a huge disappointment if he had to go into this penultimate tie without the pair.
The Hoops beat Barcelona 2-1 last week without them and now have a big chance of qualifying from Group G.
However, Lennon – who has had to rule out Emilio Izaguirre with a hamstring tear for another month – wants to have as many of his big guns as possible available for the shoot out in Lisbon where a victory would book that knock out round spot.
But the update on Forrest – who has not played in any of the last four games – and Hooper – who has been out of action since the end of last month – is not good.
Lennon said: "James is a doubt for Benfica with a hamstring injury.
"We will have to see how he is over the next week or so.
"With Gary, it is going to be a race for him to make the Aberdeen game on Saturday or the match in Lisbon the following Tuesday.
"He is also out with a hamstring injury.
"They need to be 150 per cent right because hamstrings are such delicate injuries and there is the chance of re-tearing it. It is a worry."
The manager added that, with such explosive players, who rely on bursts of speed, it is important not to rush them back.
Lenny said: "We have to tread carefully with them."
Lennon who saw Charlie Mulgrew limp out of the ground after yesterday's 1-1 draw with St Johnstone, leaving the defender doubtful for Scotland's match in Luxembourg on Wednesday, is also concerned so many of his players are off on international duty this week.
Some, like Victor Wanyama, who will represent Kenya in Tanzania on Wednesday, are being asked to travel thousands of miles to play in friendlies.
The boss can only keep his fingers crossed all return unscathed, and is planning to speak to national coaches to ask them to consider Celtic's heavy fixture schedule when they select their teams.
But there is some good news from the treatment room.
Striker Lassad Nouioui, out of action for three weeks with a groin injury, is ready to return, along with defender Thomas Rogne, who has been sidelined with a calf problem.
The manager said: "Lassad will start training today. Rogne might come into the frame as well."