The pain from the broken bone is bad enough, Kiwanuka said Saturday between practices on the second day of training camp at the University at Albany.
There is also the mental pain of missing a sport you love and then a stabbing pain when someone says that if the team won without you, you might not be needed after all.
"That guy, he put his heart and soul into the organization for a long time," Kiwanuka said of Shockey. "He was a vocal leader, an energy guy and he was kind of the face and voice of this team for a long time. So for guys to say, and people here to say we are better off without him as a player, it stings a lot, especially when you play as hard as he did."
Shockey never seemed to recover. He complained to the team about his role in the offense and later accused the organization of leaking things to the media.
When minicamp rolled around in June, he refused to either talk to the media or to stand on the field for even a few minutes to watch practice. He was nursing a badly sprained ankle at the time.
"I understand how he got to that point because like I said, it stung a little bit that we couldn't be out there," Kiwanuka said. "But it had nothing to do with the Super Bowl run. It had to do with the fact we are men with jobs, and we weren't able to produce and contribute to the team. That's a tough thing to do."
Kiwanuka, who broke his leg in mid-November, a month before Shockey was sidelined, said the tight end's life is focused on football.
"For him, everything is magnified when he can't do what he's meant to do," Kiwanuka said. "He is a tight end in the NFL and he is one of the best out there. When you are that driven and that focused on your life and your job, and everything you do revolves around that and then you can't do it one day, that's got to be tough."
Kiwanuka made the transition from defensive end to strongside linebacker last season and seemed to be learning on the job when he broke his left leg against Detroit on Nov. 18 and missed the rest of the season and the playoffs.
"The fact that I wasn't a part of it is not something I am happy about," Kiwanuka said. "At the same time, I was so proud of these guys and so proud of being a part of the Super Bowl, all the other stuff faded away when the confetti started flying."
Kiwanuka is ahead of schedule in his recovery. The Giants had planned to have him practice once at day at the start of camp, but he did make both practices on Friday and on Saturday.
"His attitude is this: if you tell him to be in there twice, he's in there three times," coach Tom Coughlin said. "He's a very focused guy. I've looked at all of those things that happened - there is no feeling sorry for himself. He's done a nice job out here in the first few practices."
Kiwanuka has some residual effects from his injury, but insists he would be able to play if the Giants had a game.
"It has been a long time since I've been on the field," Kiwanuka said. "I'm just excited to be back out there, I'm not anxious to have any days off yet."
The former Boston College star and first-round draft pick acknowledges he still has a lot to learn about playing linebacker.
"This is my second year at linebacker and I know some people are going to get some stuff faster than I am," he said. "At the same time, I am studying (hard) and I know a lot more of the defense than I did a year ago. I am confident where I am at."