The 26-year-old Scotland international has scored only twice this season, the last of them the opener in October's 2-1 derby victory over rivals Newcastle.
Fletcher is without a goal in seven games in all competitions for the Black Cats, who have managed only seven between them in the meantime, and the former Wolves frontman is currently behind full-back Phil Bardsley in the scoring stakes.
However, Poyet, who paired the £12million signing with United States international Jozy Altidore against Tottenham last Saturday, does not believe the fault lies with him.
He said: "If he had missed a clear chance, I would have to say maybe he was lacking confidence, but he hasn't had too many because we are not creating too many.
"We are missing the last pass, cross, decision, movement. That's been missing. It's the most difficult part of any team, any game.
"There are plenty of teams out there who are decent up to a point, and then after that, you are missing that last punch and we are no different at the moment."
Poyet would dearly love to see Fletcher end his wait for a goal this weekend as the bottom-of-the-table Black Cats head for West Ham deep in relegation trouble despite the season being only 15 games old.
They have claimed just a single point from their last four league outings and their total now stands on eight, five fewer than their closest rivals, Crystal Palace, Fulham and the Hammers.
Even victory at Upton Park would not lift Poyet's men from the foot of the table, but it would go a long way towards repairing the damage of successive home defeats by Chelsea and Tottenham which left many fans fearing the worst.
Sunderland took the lead in both those games, but on each occasion, retained it for only a matter of minutes, with John O'Shea's own goal - the club's fifth this season - ultimately condemning them to defeat by Spurs.
Poyet will head south knowing a third successive defeat could see the club cast further adrift with the Hammers also fighting for their lives.
Opposite number Sam Allardyce will be without the suspended Kevin Nolan, while fellow dangerman Stewart Downing is injured and striker Andy Carroll is working his way back to full fitness after a lengthy lay-off.
Poyet admits that could work in the Black Cats' favour, although only if they take full advantage of Allardyce's misfortune.
He said: "I am sure if you are playing Barcelona, it's better if [Lionel] Messi doesn't play, and if you are playing against Real Madrid, it's better if [Cristiano] Ronaldo doesn't play.
"They are very important players, so it's an opportunity. But I am sure the players who will play are Premier League players who are going to give 100 per cent for West Ham.
"But it's not Downing, it's not Nolan, it's not Carroll - although Carroll is close.
"But we will see. On paper, it could be better, but we need to play the game the same way because they are Premier League players."
Poyet has no fresh injury problems, but keeper Keiren Westwood and defender Carlos Cuellar remain on the sidelines.