The recalled Scotland international has netted all five of the Black Cats' Premier League goals so far this season since arriving from Wolves in the summer but O'Shea feels that his teammates need to occasionally ease the burden he is faced with.
"Fletch has been amazing but there's pressure on us all, including us defenders to pop up at set pieces and score goals," O'Shea told the club's official website.
"I nearly got one on Saturday and we should be with the fantastic delivery we have from the likes of Adam Johnson, James [McClean] and Seb [Larsson].
"We should be scoring more goals from set pieces and that's something we're looking to improve on.
"Hopefully it will happen because we can't keep expecting Fletch to bang in our goals."