Stephen A. Smith says that he isn't concerned with Andrew Luck's lower leg injury because he has faith in the Colts' ability to protect him in games. (2:04)

Despite Andrew Luck's prolonged absence and confusion about a lower left leg injury, the Indianapolis Colts have a "guarded optimism" about the quarterback's availability to open the regular season, according to sources familiar with the team's sentiments.

Colts coach Frank Reich said this week he would like to know following the team's third preseason game, Aug. 24 against the Chicago Bears, who will line up at quarterback for Indianapolis' regular-season opener. Reich wants to see enough progress to feel better about Luck's chances, a source added.

Colts general manager Chris Ballard said earlier this week that tests done on Luck on Monday night revealed the quarterback has gone from dealing with a calf strain, with which he originally was diagnosed in March, to having pain in the "high anklish" area of his left leg.

Ballard said Luck will not play in the preseason.

Luck, 29, has been diligent in his rehab and has been working with independent throwing tutor Tom House, per sources. There has been enough progress that has encouraged "guarded optimism" but, as one source clarified, it is nothing more than that until the Colts see Luck on the field working with the team.

The Colts' first regular-season game will be Sept. 8 on the road against the Los Angeles Chargers.

Jacoby Brissett will be the starting quarterback if Luck is not ready.