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. "He's not training tonight, we will leave him out as a precaution, and we will make a decision in the morning about him."
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.
King will be without suspended duo John O'Shea and Richard Dunne for the clash against group leaders Germany, with Sean St Ledger and Ciaran Clark set to deputise in central defence.