"I've said it a million times, it's hell getting old," Jones told the Atlanta Journal-Constitution.
Jones, who sounds as if he's leaning increasingly toward retirement after this season, added: "Tomorrow might be my last day. I don't know. I don't really focus on it that much. The body is starting to tell me every morning when I wake up that it's getting close. I'm signed through the end of this year. If I play in a certain amount of games, I got an option for next year. I don't know what next year entails.
"I don't know if I can make it through this year."
Jones' contract will pay him $14 million in 2012, and includes a $7 million option that will vest at $9 million if he plays in 123 games this season.
In 2011, he played in 126 games and hit .275. He credits his teammates as the reason he returned.
"The big reason for me coming back was my teammates wanted me to come back," he told the Atlanta Journal-Constitution. "I still feel like I can be a productive major leaguer. We'll give it this year and see how it feels."
The likely future Hall of Famer is 0-for-8 in four games so far this spring, with three walks. He missed five games with leg soreness.
"... I knew it was going to be hard coming into spring. But I was nowhere close to being ready," he told the paper. "For the first 10 days we were here, it was painful. As long as I can take care of my knees. My knees have given me the most problems through the years. I dare say if I hadn't had five knee surgeries I'd be getting around a little better and I'd be feeling a better about things going on my 40th birthday.
"As I alluded to earlier, this game is going to wear you down, whether you have major injuries such as two torn ACLs, menisucus tears -- I've got no meniscus in the right knee. That takes its toll. I've got to go when I can go and tell (manager) Fredi (Gonzalez) when I can't."