Fletcher has not played since March after damaging ankle ligaments whilst on international duty with Scotland but has undertaken an intensive rehabilitation over the summer.
"His improvement has surprised everybody - we are happy, but more importantly he is happy and excited," the Sunderland manager said.
"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."