Dwight Howard is believed to be seeking a maximum contract extension in July. (AP)

The Houston Rockets have started contacting teams about trading eight-time All-Star Dwight Howard, league sources told The Vertical.

Howard, 30, plans to exercise an opt-out in his contract this summer to become an unrestricted free agent, and uncertainty surrounding the commitment both sides are willing to make has pushed Houston general manager Daryl Morey toward seeking potential trades on the market, league sources said.

The NBA’s trade deadline is Feb. 18.

The Rockets are working with Howard’s agent, Dan Fegan, on possible destinations, league executives told The Vertical.

Howard is believed to be seeking a maximum contract extension in July.

The Rockets have struggled to a 27-28 start to the season, including a 116-113 loss to the Portland Trail Blazers on Wednesday night.

Upon leaving the Los Angeles Lakers in 2013, Howard signed a four-year, $88 million contract with the Rockets. The deal included a player option for the 2016-17 season.

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