Polian said Clark was expected to meet with doctors on Thursday for a second opinion and to determine a timetable for his recovery, according to WISH-TV in Indianapolis.
The length of Clark's absence is uncertain, as is the exact nature of his injury.
"He's being evaluated," Colts coach Jim Caldwell said Wednesday when asked about Clark's injury.
The Colts believe they'll have the definitive word on Clark's injury and absence by Thursday, regardless of what the third opinion says, ESPN senior NFL analyst Chris Mortensen reported. Surgery is being discussed.
Earlier Wednesday, the Colts re-signed tight end Gijon Robinson, who was waived earlier this year.
Adam Schefter is ESPN's NFL Insider. Inrformation from ESPN senior NFL analyst Chris Mortensen was used in this report.