McGregor has been ruled out for four to six weeks with a shoulder injury meaning 39-year-old Harper will come in for his first Premier League start of the season against Crystal Palace on Saturday.
Harper will see first team action for up to six weeks.
Steve Bruce: “Harper will give us that experience that we saw last year, he came into the fray and did fantastically for us.
“I wish he was a few years younger, I’m sure he does too but he’s a very good goalkeeper.”