Dukes rebounded in June, hitting .292 with 4 home runs for the month, before injuring his knee on July 5, 2008 in a game against the Cincinnati Reds. He had surgery on his knee, and then returned on July 31, 2008, much earlier than expected. Dukes landed on the disabled list yet again with a calf strain shortly thereafter, on August 7, 2008. Dukes returned to the Nationals on August 26, 2008 and hit .267 with 7 home runs and 26 RBI over his last 29 games.