Lenahan, 23, a sales executive for General Mills in Dresher, and his brother Lawrence, 26, an Air Force captain, decided to make the trip together.
They almost made it through the entire race Thursday morning when a bull that broke loose from the pack gored both of them. Michael was struck in his right leg and Lawrence in his left buttock.
Both brothers are at the Hospital de Navarra in Pamplona. Their condition could not be immediately determined, and the family was awaiting word from doctors there.
Michael's girlfriend, Erica Messina, of Stamford, Conn., said that she has spoken with him and that "he's in better spirits today, but still doesn't know when he's going to be released."
Said Lenahan's father: "He said they're big animals and when they're coming at you, there's nothing you can do."
The bull-running event, part of the San Fermin festival in Pamplona, gained worldwide fame in Ernest Hemingway's 1926 novel The Sun Also Rises. Thirteen people have been killed in the event since record-keeping began in 1924.
Larry Lenahan said both injured sons - the family includes another son and a daughter - embraced outdoor activities at an early age.
Both are licensed pilots - Lawrence, nicknamed Sean, is an Air Force Academy graduate - and love to canoe, ski, scuba dive and play sports. Michael briefly played varsity soccer for the University of Pennsylvania.
"When all the kids were about 2 years old, I took them all skiing. I'd go on a black - we only do black and double-black - trail and go without poles and hold him in my arms while I skiied down," Larry Lenahan said. "I think that helped them get used to it."
His daughter, Shannon, said her brothers have always been close.
"It was originally Sean's idea to do the running of the bulls. He's always wanted to. It's been a dream of his," said Shannon, 22.
Larry Lenahan said Shannon might go to Spain to help her brothers get home because he has engagements this weekend with his youngest child, Keven, whose 15th birthday is today.
In the fall, Sean plans to leave the Air Force to attend the Wharton School of Business at the University of Pennsylvania. He and his brother hope to live together in Center City, family members said.
A supervisor in Michael Lenahan's office, Steve Mayle, released a statement that said: "Michael is an adventuresome employee who certainly takes life by the horns. We don't want to poke fun at his situation, but we do wonder if he ate his Wheaties for breakfast that morning."
Contact staff writer Katie Stuhldreher at 215-854-2601 or firstname.lastname@example.org.