He had been with 888.com for more than five years and was previously UK marketing manager.
It is unclear at this stage if he has been replaced or whether he has a job to go.
Robinson led the search for a new agency last October which resulted in Grey being appointed at the start of the year.
However, it emerged this week that 888.com has called a new pitch for its £3m advertising business after incumbent Grey resigned the account.
It is believed that the breakdown in the relationship was a dispute over fees.
In April, Grey unveiled it first work for 888.com since its appointment, a push for female-targeted bingo site 888.ladies.com.
The TV ads featured so-called “Bingo Superstars” that develop delusions of grandeur after winning at bingo
Last year, 888.com pulled out of its sponsorship of the Snooker World Championship just two years into its five-year contract.
An 888.com spokesman confirmed Robinson’s departure, but declined to comment further.