Thomas, a second-round draft pick (No. 30 overall) out of Kansas State, missed Miami's season opener because of his injury, and he aggravated it this week. His absence likely means playing time for Steve Slaton, whom the Dolphins claimed off waivers Wednesday.
Slaton rushed for 1,282 yards as a rookie with the Houston Texans in 2008, but he was less productive after injuring his neck in 2009 and was released this week.
The Associated Press contributed to this report.