The Black Cats have only mustered three goals in the league this season, but the Italian hopes the striker, who has returned from a long-term injury, can improve their fortunes
The Black Cats are propping up table with one point from four league matches, but Di Canio believes his team have a big opportunity to move above 19th-placed West Bromwich Albion when the bottom two sides clash at the Hawthorns on Saturday.
Fletcher will be key to Sunderland's chances, according to Di Canio, with the 26-year-old Scottish striker still working his way back to full fitness after suffering a serious ankle injury in March.
"He has the killer instinct in the box that we need," Di Canio was reported as saying by The Irish Mirror.
"But we have a methodology with our players and we won't play him if he is not sharp enough.
"We want Fletcher to be sharp for six or seven months, not just one or two. Consequently, we will do what is best for the season as a whole, not just the next two or three games."
Fletcher made his comeback in Sunderland's third game of the season, scoring after coming on as a substitute in a 3-1 defeat at Crystal Palace, before starting in a 3-1 home loss to Arsenal on Saturday.
Di Canio's men have scored just three goals this season, with only West Brom (one) and 16th-placed Hull City Tigers (two) having managed fewer.
Despite his team's struggles up front, however, Di Canio will not rush Fletcher if he is not ready to take on the Baggies.
"He scored an excellent goal against Crystal Palace but we have to remember he has been out a long time and not had the benefit of a full pre-season," he added.
"We cannot expect him to be consistent immediately. When you come back from a long injury, adrenaline helps you a lot but players are not machines.
"We have to handle him sensibly and he has done a sort of mini-pre-season with [coach] Claudio Donatelli but not had the double sessions of other players."