Simpson was hampered by the problem in the latter part of last season and said on Thursday that the injury was still an issue.
"I've had a bit a foot injury actually this pre-season and it's still lingering," Simpson told afl.com.au.
"I can't get rid of it and I'm hoping (it will improve), but if it doesn't go by the end of next week, then I will have to do something about it, but it's still lingering around at the moment.
"It's giving me the s****. I don't know what's going on at the moment with it, so I'm hoping it will be resolved by the end of next week.
"That (the foot injury) and I hurt my ribs (in 2005), buggered up the last half of the season, personally, but other than that, the body is going well."
The much-admired Kangaroo leader is also struggling to restrict himself to just the modified program.
"I can just do the straight running, but when training picks up, I just find that I get a bit sore after training," Simpson said.
"It might be a good thing. I'm 30 this year, so I'm used to doing everything at training and going full-tilt, but it's been a little bit different this year and maybe it might help me out towards the end of the season.
"I normally tire a little bit (at the end of the season), so this time around, I'm hoping I might finish it off a bit stronger."
Simpson said that before his injury he rarely missed a beat during any training sessions.
"I've never missed a training session pre-season, let alone games, so it's just something I'm starting to get used to now," Simpson said.
"I used to keep training until it got better and the last couple of injuries aren't getting better, so I'm learning slowly that you've got to perhaps give your body a rest every now and then.
"I like to be out on the track and you miss the boys when you're not out there, so it's something I'm getting used to."
Aside from his injury, Simpson said the majority of players were healthy, despite some players also being on modified programs.
"I'm on my own in rehab, but Jonny Hay is on a modified program. He came across (from Hawthorn) with a few little niggles and the coach and the medical staff really look after the players that need to be monitored," Simpson said.
"They've done really well with how they've looked after him, and Jade Rawlings and a couple of other players are on modified programs - they're not injured as such - but their programs have been modified."
