"I haven't had any setbacks, everything is good and positive, but I don't want to screw up and come back too early before it's ready," Hart said.
Hart had surgery Jan. 25 to repair a meniscus tear and, more significantly, debride the knee joint surface to repair a crack. Doctors induced bleeding to fill in that small gap and predicted a four-month rehab. Hart said at the time he was aiming to shave a month off that timetable.
He had a favorable MRI scan March 8 and abandoned the crutches he'd been using, but has been limited to range-of-motion exercises and strength building since then. Hart has yet to get on a treadmill.
"I still think I can come back a little earlier," Hart said. "I'm definitely optimistic, but I was maybe overshooting when I was talking about playing in April. I probably could; I just might be nervous. Whenever I can do the movements I need to without feeling weak, then I'll have a better idea."
Alex Gonzalez and Taylor Green appear the most likely candidates to fill in at first base, barring an outside acquisition.
Adam McCalvy is a reporter for MLB.com. Read his blog, Brew Beat, and follow him on Twitter at @AdamMcCalvy. This story was not subject to the approval of Major League Baseball or its clubs.