Ibrahimovic and Messi have struggled to recover from thigh injuries in time for the penultimate Group F game which Barca really need to win to continue defending their European crown.
The champions are third behind Inter and Rubin Kazan and a defeat would put them out if Rubin beat Dynamo Kiev.
"We won't know until tomorrow. We are doing all we can for them to be available. The medics haven't told me one way or the other," Guardiola told a news conference.
"Whoever plays, we are all in it together, and I don't know why we can't win without them. But you always notice it when you are without your best.
"We have two games left and we need four points. Every team has a chance, but it is in our own hands."
ETO'O RETURNS
Ibrahimovic trained with the rest of the squad on Monday evening, while Messi worked apart, but Guardiola also has to worry about the visit of new La Liga leaders Real Madrid for their top-of-the-table clash on Sunday.
The return to the Nou Camp of Samuel Eto'o in an Inter shirt has been another talking point in the build up to the visit of the Serie A leaders.
The Cameroon striker spent five years at Barca, helping them win two European Cups, before leaving in the swap deal that brought Sweden's Ibrahimovic in as his replacement.
"He (Eto'o) will get the reception he deserves, and he deserves a good one," Guardiola added of his former number nine.
"The fans understand the player was not responsible for his exit, his coach was."
Earlier, Inter manager Jose Mourinho, who had already said he was convinced Ibrahimovic would feature, played down the significance of the doubts over the fitness of Argentine Messi.
"I'm not worried about whether Messi will play or not. It doesn't change my plans," the Portuguese said.
"The world of football hopes to see Barca continue in the Champions League. They are the best team in Europe and they don't appear to be scared of us, but neither are we of them."
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