Clark was drafted by the Indianapolis Colts of the NFL in the 1st round (24th overall) of the 2003 NFL Draft. In Indianapolis, Clark wore #44. As a rookie, Clark started 10 games and had 340 receiving yards before his season ended with an injury. Clark continued his solid production over the next couple years, and in 2004 had an 80 yard touchdown, which is "extremely" rare for a tight end.