The 33-year-old injured his ankle on Tuesday and sat out training at the Rhein Energie Stadion on Thursday evening.
Interim boss Noel King says he will leave it until matchday before making a final decision on Keane's participation.
"He has a bit of an ankle problem," said King on Thursday. "He's not training tonight, we will leave him out as a precaution, and we will make a decision in the morning about him.
"He got a little kick on it. It's something that comes and goes with him over the last number of months and he got a little kick on it, so it's a worry.
"When he wakes up in the morning, we will get at it straight away."
Keane to stay with squad
Earlier in the week, King announced that he had turned down a request from Keane's club manager at LA Galaxy, Bruce Arena, for the player to return early.
The Galaxy boss had asked if Keane might be released after the Germany match but King has decided the player will remain with the squad for next Tuesday's game at home to Kazakhstan.
He explained on Thursday: "He is healing, and that's the process, so he's being tended to and we are hoping he will be ready for tomorrow. If he doesn't make tomorrow, we are hoping he will be ready for the next game.
"There's no question of going home or anything like that. He's still in the squad."
Trio in contention to stand-in for Keane
Anthony Stokes, Shane Long or Kevin Doyle will vie to start if Keane misses out but King says Ireland's record scorer would be a big loss.
"Robbie been one of our leading lights over the years, he's the leading scorer, one of the leading scorers in Europe," he said.
"If he doesn't make it, we wouldn't be happy about that, that's for sure, but we would get on with it.
"There's nothing we can do about it. If he goes, he goes, and the person who comes in will be delighted with the opportunity and delighted with the cap."
Asked whether Keane would have a painkilling injection in an attempt to play, King added: "That would be a medical situation, that would be for (medical director) Alan Byrne, Robbie and his club.
"We wouldn't do anything without talking to the Galaxy. They know about the situation, so that would be pretty much out of my hands."
King gave little else away about team selection, although the presence of Crystal Palace defender Damien Delaney at the press conference suggested he will start at centre-back in the absence of the suspended Richard Dunne and John O'Shea.