Manning was diagnosed with inflamed tissue in his right foot late Monday following an MRI at the Hospital for Special Surgery in Manhattan. It's a problem that usually develops over time and lingers.
ESPN senior NFL analyst Chris Mortensen first reported the diagnosis.
Team physician Russell Warren told Manning he could play this weekend against the Oakland Raiders if he could tolerate the pain.
"It's not as serious an injury as [the doctor] has seen before, where it's the whole foot that's hurting," Manning said in an interview on ESPN Radio in New York. "It's just kind of a portion of it."
The Giants (4-0) have listed Manning as day to day with the plantar fasciitis, which has caused soreness and swelling in the heel and arch area on the bottom of his foot.
Dr. Steven Weinfeld, chief of foot and ankle surgery from Mount Sinai's Department of Orthopaedics in New York City, said in a telephone interview with The Associated Press that the injury could be treated by taping the foot, stretching, cushioning the area and using ibuprofen or any anti-inflammatory medicine. He said cortisone injections also can help.
The past 24 hours have been a scary time for Giants faithful, knowing an injury could suddenly elevate veteran David Carr to the starting job this weekend against Oakland, and a serious injury could crush hopes of another championship run.
Manning, who has thrown for 1,039 yards, eight touchdowns and two interceptions this season, was hurt early in the fourth quarter in a non-contact injury in New York's 27-16 win over the Chiefs in Kansas City.
The MVP of the Super Bowl in February 2008 made a fake on play-action and went back to throw. As he planted his right foot, he suddenly hopped as if he had stepped in a divot or something popped. He threw an incomplete pass to Steve Smith seconds later.
The play reminded many of the season-ending Achilles tendon injury former Jets quarterback Vinny Testaverde suffered at the start of the 1999 season.
"Of the things it could have been, it's one of the better ones," Weinfeld said of the diagnosis.
While the words were comforting, so was the sight of Manning standing in front of his locker earlier in the afternoon with neither a boot, a crutch or much evidence of heavy tape on his right foot.
The only obvious sign of an injury was a slight limp when he walked away.
"Yeah, that's all positive stuff," Manning said. "I think it's just time and ice and some treatment here and at home, kind of nonstop everything for the next couple of days. My goal is by Wednesday to be practicing and get out there and not being restricted."
Manning admittedly was concerned about his Achilles tendon briefly after his incomplete pass to Smith. He threw a touchdown pass to rookie Hakeem Nicks on the next play and then spent the rest of the game on the bench.
"I knew what it was," Manning said. "I knew it was the bottom of my foot, my heel area. I could walk around a little bit. It was good that we got a touchdown on that play, kind of gave ourselves a pretty good lead at the time."
Manning, who has started 82 consecutive games, still had some swelling and soreness Monday morning. He got ice and stimulation treatment and went through his strength program before attending meetings and talking to the media.
"It doesn't feel any worse today than it did yesterday, which is a good sign," Manning said. "Hopefully, it just gets better every day."
Manning has played through pain. He injured the A-C joint in his right shoulder in a game against Dallas early in 2007 and came back the following weekend to play against Green Bay.
"The last time, with the shoulder, [the doctor] said I'd be out a month and I played the next week," Manning said, noting Warren told him this time it's just a matter of how fast can he heal.
Coughlin said Manning is one of those players who wants to be out there with his teammates.
"I am not worried about him," guard Rich Seubert said. "A couple of years ago, he had the shoulder or whatever it was and he was fine and didn't miss anything. Then I let [Browns nose tackle] Shaun Rogers fall on him last year. He's a tough kid. I know on Sunday he will be out there playing with us."
Carr, the No. 1 pick overall by Houston in the 2002 draft and a veteran of 79 NFL starts, is ready just in case.
"I have done this before, it's not my first rodeo," Carr said. "I have a great team around me, that's the biggest thing. I think we have the best offensive line in football and throwing to some young receivers that are really excited to play, exciting to watch, exciting to throw to. I got a chance to throw to them a little bit in preseason and every day in practice, so it should be exciting. We have a good football team. I just have to go in and do my job."
Information from The Associated Press was used in this report.