Johnson raised doubt over whether he would stay in Houston by suggesting that it could be time to look elsewhere following another disappointing campaign in 2013.
The seven-time Pro Bowler is yet to submit a formal request for a trade but failed to turn up to the first day of the OTAs this afternoon.
"I have a ton of respect for him. We'd love to have him here now. That's up to him," O'Brien told reporters.
Johnson holds almost every receiving record in Texans history, having joined them as the third overall pick in the 2003 Draft.