Brown isn't in pain, but cannot complete a pushup and, with a four-month recovery time, is likely headed to injured reserve, according to the source.
"We're looking at what could become available over the next couple of weeks and we'll shuffle some guys around," Whisenhunt said, according to The Associated Press.
Brown's injury serves as a reminder that the NFL and NFL Players Association have not yet finalized injured-reserve exemption rules that were voted on by the owners in May.
A first-round draft pick out of Penn State in 2007, Brown spent the first three seasons of his NFL career at right tackle before moving to the left side in 2010. He has struggled with the move.
According to the Football Outsiders Almanac, Brown has had back-to-back seasons with double-digit blown blocks that led to either sacks, intentional groundings or holding penalties.
Brown did show some improvement over the second half of the 2011 season and, after being released for salary-cap purposes before the start of the 2012 league year, was re-signed to a five-year, $30 million contract that included $12 million in guaranteed money.
If Brown does land on injured reserve, the Cardinals don't have many appealing options to protect John Skelton or Kevin Kolb's blindside and could pay the price for being one of just two teams that haven't used a first-, second-, or third-round draft pick on an offensive linemen in the last five NFL drafts.
D.J. Young replaced Brown on Friday night, but the former undrafted free agent from Michigan State spent 16 of 17 weeks last season on the practice squad and hasn't appeared in an NFL regular-season game.
Seven-season veteran D'Anthony Batiste is another option to take Brown's spot, Whisenhunt said.
Free-agent options are limited.
Former San Diego Chargers left tackle Marcus McNeill retired for health reasons last week, and any starting-caliber left tackles who are available right now (Chad Clifton, for example) have some form of baggage (age, health, performance) with them.