He gave a tentative assessment of Fletcher's progress after the Scottish international made his highly-anticipated return to action during the Reds' pre-season testimonial defeat to Aberdeen.
"Darren's fantastic, I mean obviously we are in the laps of the gods in terms of Darren because he has a certain condition that he has to handle very well," Sir Alex told MUTV.
"At the moment he is doing very well at that, he has put the weight back on which was a big concern for the kid. But he came on for 25 minutes in Aberdeen and did very well. He trained yesterday so he is fine."