McClean burst onto the scene last term with a series of dynamic displays but he has struggled to recapture his best form at the start of the new campaign.
"James is a marked man this year. And he is probably going through a phase where he needs a deflection to go in to boost his confidence again," said O'Shea in the Daily Star Sunday.
"The demands when you have established yourself are higher but he is more than capable of dealing with those because he is doing the right things in training. We will soon see the benefits."
O'Shea admits it has been a frustrating period for everyone at the club this season as results have been so disappointing, with the Black Cats languishing in 16th place ahead of Sunday's match against Fulham.
They have scored just seven goals in ten games but O'Shea remains convinced they will soon get back on track and start climbing the standings.
"With the squad we have, we should have done better this term. The league table doesn't lie but we're getting things together now with our performances," he said.
"We have a good enough team and a good enough squad but just need that one result to give confidence to everyone again and to show that we should be higher up the table than we are now."