Adela Dworin, president of the Hebrew Community of Cuba, told Reuters that Gross, 63, was "very depressed" when she last saw him in May, but this time was smiling and more hopeful about the future.
Her description of Gross conflicted with that given by his wife, Judy Gross, who said after a recent visit she was "devastated" by his appearance.
The Cuban government has said that Gross is in "normal" health and getting lots of exercise.
"We found him to be in good spirits," Dworin said in a phone interview. "He was doing much better this time, maybe because he believes President (Barack) Obama will be re-elected and that in the next four years relations between Cuba and the United States will improve."
Dworin said she and group's vice president, David Pristein, visited Gross to mark this week's Jewish high holiday Yom Kippur.
Gross has been jailed in Cuba since December 2009 in a case that put the brakes on a brief improvement in long-hostile US-Cuba relations.
He was installing Internet networks for Jewish groups under a semi-covert US program promoting political change on the communist island.
A Cuban court sentenced him to 15 years behind bars in a March 2011 trial.
Judy Gross said on September 11 her husband had lost 105 pounds (48 kg) during his incarceration, was suffering from degenerative arthritis and had a "mass" on his shoulder.
"While his spirit remains strong, I fear he is not going to survive this terrible ordeal," she said in a statement issued by Jared Genser, the family's recently acquired lawyer.
Dworin said Gross told her he weighed 147 pounds (67 kg) and had an arthritic hip, but also was lifting weights and doing a lot of walking in a patio at the hospital.
Two photos from the visit showed the once portly, but now gaunt Gross wearing blue jeans and a blue guayabera shirt, accompanied by Dworin and Pristein in a visiting room with black chairs, green walls and a potted plant.
"He looked very agile to me," Dworin said. She said Gross told her the "mass" on his shoulder had been examined by Cuban doctors, found to be benign and the results of the tests sent to the United States.
Genser has demanded, so far unsuccessfully, that he be allowed to send a doctor to Cuba to examine Gross.
Dworin said she and Pristein sang a Yom Kippur song with Gross and talked for two hours about issues ranging from his health to the US elections to his interest in Cuban baseball and his love for Cuba, despite his circumstances.
"He said that he and his wife both love Cuba and maybe one day they will return to the island for a second honeymoon," Dworin said.
Dworin said it was the seventh time she had visited Gross and would do so again in December during Hanukkah.
"I want the world to know that the Cuban Jewish community has not abandoned Alan Gross, ever," she said.