The Hammers are currently in seventh place in the Premier League table after taking 10 points from their opening seven games of the campaign.
McDonald believes that strong player recruitment and a change in tactics have contributed significantly to the team's success this term.
When asked if their impressive form has been unexpected, he told the club's official website: "Not really. It's disappointing that we haven't got a couple more points on the board. I'm pleased with the points we do have. We've picked up our first away win of the season and now we've won two on the bounce at home which is great. That gives confidence to everybody for the rest of the season.
"I think personnel recruitment has been very good over the summer. I've been at the club for almost four years now. In that time even the way people come in has changed.
"We've also changed the formation round a little bit and the style. I think last season we scored a lot of goals from open play and then injuries slowed us down. In the end we didn't get as many points as we should have done."
West Ham are back in Premier League action on Saturday when they make the trip to struggling Burnley.