Dr. James Andrews, a noted orthopedic specialist in Birmingham, Alabama, studied an MRI of Manning's shoulder and informed the team that he believed Manning was "week-to-week" based on his findings, a source said.
However, two sources said again on Tuesday Manning does have a slightly separated shoulder. The Giants have varied on their official report, calling it either a contusion of the A-C joint or a shoulder sprain.
"It's medical word games," a source close to Manning said. "He's got a second-degree separation -- that comes from the Giants' doctor [Russ Warren], who did the hands-on exam and thought it could be a month three or four weeks.
"Dr. Andrews admitted that he doesn't have the benefit of a hands-on exam, but he was encouraged by the MRI. There's no structural damage, but there is a little soreness and some swelling. He thinks that it could be a week-to-week deal, but that's not an absolute. It's encouraging but there has to be some caution exercised here."
Manning himself has said that he was not in a great deal of pain and believed he has a chance of playing Sunday against the Green Bay Packers in a home opener.
Chris Mortensen covers the NFL for ESPN.