The Tottenham Hotspur player hurt his left elbow in training on Wednesday.
Keller was in too much pain to undergo an immediate scan. But hospital tests have now revealed nothing more serious than bruising.
And US coach Bruce Arena said that Keller was still in the frame with Blackburn's Brad Friedel for a place in the team to face Portugal on 5 June.
"Kasey's injury, from what I understand at the moment, is nothing that we need to be concerned about in the long term," Arena said.
"It's something of the short term and whether that means another day, another few days, three days, four days, who knows.
"We have to see how he responds to treatment but we are not concerned that Kasey's injury is one which is going to interfere with his ability to play in this World Cup."
Arena expects to have finalised his opening line-up by Sunday.
And he indicated that Keller is still rivalling Friedel for a place in the side.
"We haven't made a determination what we are going to do," he said.
"I think they are both quality keepers and I think you'll see in this World Cup that there is going to be a number of countries that are going to use more than one goalkeeper."