The Black Cats are currently just one place an one point above the relegation zone in the Premier League table following two wins from their opening 14 matches.
"It's been a tough start to the season. It hasn't come as any major surprise to me," O'Neill told reporters.
"The team is essentially the same as last season so it's a tough struggle, but we'll get there."
Sunderland can pull away from the drop zone on Saturday with a victory against an out-of-form Chelsea at the Stadium of Light.