The injury was caused from irritation when he drags the foot while throwing a pitch. Harrison is flying to Dallas on Monday for an evaluation by an orthopedist.
"I'm just trying to figure something out to get the inflammation to go down," Harrison said. "It's minor. I'm just glad it isn't anything bad."
This is a recurrence of a problem that first emerged last season and was solved with a custom orthotic that was inserted into his shoe. Harrison said the irritation flared up again about two weeks ago for the first time since addressing the problem last season.
The inflammation is not related to a turf-toe injury he suffered in 2007, although it is on the same foot. He believes this problem can be solved with a new orthotic insert.
"I need to fix it now during spring training. This way I don't have to worry about it," Harrison said. "If this was the regular season, I'd put anything I had to in there, so I could get out there. Right now, I don't need to."
Harrison is expected to rejoin the Rangers in Arizona on Monday night.