The former President broke his C2 vertebrae in his neck. He was never disoriented and the injury did not result in any neurological problems, his spokesman Jim McGrath said.
"It is a significant injury, but right now the President is in excellent shape, and we would anticipate that he would make a full recovery," Dr. William D'Angelo, his attending physician at Maine Medical Center in Portland, said Thursday. "He is doing great. His spirits are good."
"We are not expecting a long stay," McGrath said, though he added Bush would be treated with a neck brace.
A spokesman for George H.W. Bush's son George W., known as 43 because he was the 43rd President, said he was monitoring the situation from Texas.
"43 is in Dallas. He's been keeping tabs on 41 through this mom. 43 is grateful that 41 is getting such great care in Maine and is on the road to recovery," George W. Bush spokesman Freddy Ford told CNN adding "43 has spoken to 41 and said he sounded strong."
Bush's grandson, George P. Bush, summarized his grandmother's reaction: "Barbara Piece Bush declared: 'A slip and fall is not going to take out a World War II pilot.'"
He will be fitted for the brace and continue physical therapy.
"The plan is to let this injury heal on its own without surgery," McGrath said. "The president never lost consciousness, and the injury he sustained neither impinged on his spine nor resulted in any neurological deficits. He continues to have normal use of his limbs."
D'Angelo told reporters in a news conference Thursday "he is a tough guy. I am impressed." Besides the neck brace now, Bush will be in an extended brace when he is up and around. Speaking generally, D'Angelo said it usually takes a patient in his 90s about three to four months to heal from this type of injury.
President Barack Obama phoned the former President on Thursday morning to wish him a "speedy recovery" and extend his best wishes on behalf of him and the first lady, according to Eric Schultz, White House deputy press secretary.
George H. W. Bush's son Jeb, who is currently running for president, said during a campaign stop in San Francisco of his dad's injury: "He can't walk, so I think he was being picked up, and he's a big guy now, and I think he fell and cracked the second vertebrae. The bone, thankfully, not the nerve endings. And so he's in some pain and discomfort, but I think he's in pretty good shape. It's kind of hard to deal with this when I'm out and about here."
"Based on the fact that they expect him to go home quickly, based on the fact that they're not planning any operation, they're just going to treat him with a neck brace that does sound positive," CNN's Chief Medical Correspondent Sanjay Gupta said Thursday on "New Day."
Bush last month just turned 91. He revealed several years ago he suffers from a form of Parkinson's disease, which has left him unable to walk, so he gets around either in a wheelchair or a scooter.
"He's 91 years old, he's going to heal more slowly than other people, people who have fractures in the neck, people who have fractures in the hip, things like that," Gupta said.
He was hospitalized in 2014 after suffering a shortness of breath. In 2012, he was in the hospital for several months after he contracted bronchitis.
Bush and his wife last week appeared at several events in Maine with hundreds of his son Jeb's top donors to his presidential campaign.
The Bush family tweeted its thanks and thoughts Thursday morning.
Jenna Bush Hager wrote: "Always touched by kindness: thanks for all of your thoughts+prayers for our dear Gramps. We are optimistic that he will heal well."
Former Republican nominee Mitt Romney made an allusion to Bush's past as a U.S. Navy pilot in World War II: "Shot down and rescued, parachuted and landed safely, @GeorgeHWBush yesterday takes a fall. May he be victorious again, I pray."
Bush has continued his adventurous ways, even as he cracked 90 years. Last year, to celebrate his 90th birthday, the former president went skydiving. He has previously parachuted seven times, including for his 75th, 80th and 85th birthdays and when he was shot down in.