O'Brien discussed Clowney's expected return on Sunday after Houston's second day of camp.
The No. 1 overall pick in last year's draft was placed on the physically unable to perform list just before camp began.
Clowney played just four games as a rookie last season before having season-ending microfracture surgery in December. The Texans have said that his rehabilitation from that surgery is going well and they hope that he'll be ready to play in the season opener.
The Texans' first preseason game is Aug. 15 and they open the season on Sept. 13 against the Chiefs.
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