The NFL issued its notice after the Tennessee Titans returned eight positive tests, forcing them to close team facilities and jeopardizing their availability for Week 4. The Minnesota Vikings played the Titans in Week 3 and also had to shut down their facilities.
"We got a phone call early from the league about Tennessee and Minnesota," O'Brien, who serves as head coach and general manager of the Texans, told reporters, according to Aaron Wilson of the Houston Chronicle. "We decided we had a bunch of guys ready to work out, instead of keeping them holed up in a hotel, better to cancel the workouts. Earl Thomas is a hell of a player, great career."
A report Tuesday claimed the Texans called off Thomas' workout after determining he'd be a poor fit. The veteran safety was cut by the Baltimore Ravens in August following a fight with a teammate in practice. He was rumored to be an unpopular figure in the Ravens' locker room.
"We'll see where it is going forward," said O'Brien. "I have a lot of respect for Earl."
Thomas posted 49 tackles, two interceptions, and one forced fumble in 15 games for Baltimore. The seven-time Pro Bowler picked off 28 passes over nine seasons with the Seattle Seahawks.
Through three weeks, the winless Texans have zero interceptions as a team and rank 29th in points allowed.