Doctors discovered a small growth last week after Heyward complained of blurred vision in his right eye. He underwent an MRI and CAT scan, and tests showed the tumor is pressing on the optic nerve.
"I can see that ugly outfit you've got on," Heyward told a reporter during a stop in the team's locker room. "I'm always in a good mood. It's out of my hands, I can't control it. It (surgery) is something we have to do."
Heyward, 32, was placed on the non-football injured list on Monday, which ended his season. The Colts signed fullback Kantroy Barber off Buffalo's practice squad to fill the roster spot.
"It's kind of shocking to go from a routine eye check to just now, `Oh, we have a growth on the skull.' Being a football player, it kind of hurts you more than helps you," Heyward said. "I've always been a guy if I had a slight ankle sprain I would treat it myself."
Heyward said he feels very comfortable with the doctors who will do the surgery Thursday.
"I try not to know nothing about it, the more I know about it, it scares the hell out of me," he said. "I just say, tell my wife. ... I don't care if you have to open me up with a butter knife, do what you have to do."
Meanwhile, the Colts dropped to 1-8 with a loss to Miami on Sunday without Heyward. He had played in four games since signing in October and was mainly used as a blocker, gaining 15 yards on six carries.
"From a football standpoint, I don't want to take anything away from the team. The team must go on, we've got to win games, got to get better. That's a must and I've got to get better too," Heyward said.
The growth has been described to him as shrimp-sized, he said.
"That depends on what kind of shrimp you're eating," he joked. "I'm hoping it is popcorn. I'm on some medication to kind of shrink the size of it."
"He's upbeat and wants to get it over with," coach Jim Mora said. "All of us in this profession get totally consumed with it (football), everything kind of goes on the back burner. But, when something like that happens it makes you realize that there's other things more important."
Mora made Heyward a first-round draft pick for New Orleans in 1988 and coached him for five years.
"We're all hoping and praying for a successful operation on Craig," Mora said. "His positive attitude, I'm sure is going to help him through this. It's not going to be any cakewalk by a long shot, this operation. The fact that the tumor is not malignant is certainly a good sign."
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