McBreen, 36, has been allowed to join Shanghai SIPG, the Chinese Super League club where he spent five months on loan in 2013.
Last season's golden boot winner will now be ineligible for the Mariners' key clash away to league leaders Brisbane Roar on Sunday.
Earlier on Friday Central Coast confirmed the sale of star centre-back Trent Sainsbury to Dutch club PEC Zwolle, as the championship-winning side assembled by departed coach Graham Arnold continues to disband.
The Mariners, who took the unusual step of contacting supporters directly to canvass their opinion on McBreen's potential departure, claim they intend to sign several players before the transfer window shuts as they seek to replace the recent departures, which include key forward Michael McGlinchey, who followed Arnold to J-League club Vegalta Sendai.
"I can assure our fans that we are very active in the transfer market, and there will be further announcements over the next couple of days," head coach Phil Moss said in a statement.
"I have so much confidence in the squad that remains, and obviously we are in a fantastic position at this time of the season. The players that we will be bringing in will only add quality to the squad we already have."
The signing of veteran defender Eddy Bosnar, a YouTube favourite courtesy of his vicious free-kicks, is expected to be confirmed on Saturday.