The 34-year old withdrew from last Friday's Pacific Life Open quarter-final against Lleyton Hewitt but the American said it had healed sufficiently for him to take on France's Paul-Henri Mathieu in his opening match.
"It's doing better," the American said on Thursday.
"It's probably only 30 percent bigger than my other toe now, which is a big step forward. I had an MRI. Structurally, everything was sound. It just showed a tremendous amount of fluid in it."
Agassi said he would not risk playing in Miami if there was any risk of damaging his toe further.
"The pain is considerably better, and knowing that structurally nothing is going wrong with the bone or tendon gives me the freedom to push through anything I might feel. Hopefully I'll be in a position to play well."
