The Brazilian player's Web site posted a statement saying the tumor was benign, but the announcement was later removed.
"I don't think there's any question there's some positive energy, but I'm not going to interpret and analyze until we get all the information," Karl said at a workout before Thursday night's game against the Jazz.
He said the team would likely know more by early next week.
"I'm not going to play amateur doctor until I've got a lot more information than I have right now," said Karl, who has had surgery for prostate cancer.
A statement posted on the Web site and distributed by Nene's Brazilian publicist said, "According to reports presented by doctors, the exams show that the tumor is benign."
The publicist did not immediately return a call from The Associated Press.
Nene took an indefinite leave of absence Friday. There is no timetable for his return.
Asked if the team has reason to be optimistic, center Marcus Camby said, "We hope so, for him as a teammate, as a friend and as a brother."
"Basketball is secondary right now. Even without being cancerous, he's still going to be out a significant amount of time," Camby said.
Dr. Fernando J. Kim, who performed the surgery at Denver Health Medical Center, said earlier that a "right testicular mass was found incidentally and it was managed surgically."
The tumor was found last week in an exam by team physician Dr. Saurabh Mangalik.
Nene had said the tumor was found at an early stage.
"I want to thank my fans, my teammates, the Nuggets organization and everyone that's been supporting me," he said in a statement released before the tumor was found to be benign. "My victory will represent their victory as well."
Nene is averaging 6.4 points and 6.4 rebounds. He missed 22 games earlier this season after undergoing left thumb surgery. He was out for all but one game of the 2005-06 season after tearing a knee ligament, and he was sidelined for 27 games the season before with a variety of ailments.