The Iceland international scored a vital goal against Liverpool in the FA Cup when he was playing for the Royals back in 2010 which helped land McDermott a long-term deal.
Tomorrow, Sigurdsson returns to the Madejski Stadium with Spurs but McDermott feels he will receive great applause from the Reading fans for the job he did whilst with the Berkshire club.
"I owe him a lot really for what he did for me personally," said McDermott told the Daily Mirror.
"As caretaker my record wasn't very good. But I got lucky at Liverpool, he took the best penalty in the 96th minute under pressure.
"I'm sure he'll get a fantastic ovation from the fans."