In the 2009–10 season, De Laet featured in the League Cup, coming on as a substitute against Wolverhampton Wanderers and Barnsley in the third and fourth rounds and starting against Tottenham Hotspur in the fifth. Despite a defensive injury crisis in November 2009, Alex Ferguson preferred to bring midfielder Michael Carrick on for Gary Neville ahead of De Laet, after the United captain suffered a groin strain in the next league match away to West Ham United on 5 December. He then played his first league game of the 2009–10 season on 15 December against Wolverhampton Wanderers. De Laet played his second league game against Fulham on 19 December, which ended in a 3–0 defeat. On 4 May 2010, he was voted as the Denzil Haroun Reserve Team Player of the Year, beating Oliver Gill and Magnus Eikrem to the award.