Last season's top scorer for the Black Cats, Fletcher has not played since damaging ankle ligaments on Scotland duty in March.
Di Canio told the club website: "His improvement has surprised everybody. We are happy, but more importantly he is happy and excited.
"We don't have to (take a) risk. It would be silly to anticipate a time. We won't force it just because we see improvement, because another injury now could put him out for longer. It would be stupid.
"In a few weeks, maybe we can see Fletcher in action. We will keep our fingers crossed. He and the staff have done a very good job, we have handled the situation very well.
"We expect to see him in the next few weeks. I can't say two, three or four - we will see."