West Ham United travel to Crystal Palace this weekend.
Slaven Bilic's side travel to Selhurst Park on Saturday evening for a London derby.
The 28-year-old defender spent eight years with the East London club, and Sullivan is hopeful that the visiting fans give their club's "great servant" a rousing reception.
"This will be the first time that we will be facing James Tomkins since he left the Club during the summer," he told West Ham's website.
"James was a great servant to West Ham United and made a lot of friends during his long spell at the Hammers.
"I hope that James will get a great reception as he was always very loyal to the Club and only left to pursue regular first-team football."
Tomkins aside, West Ham need a win and badly. Bilic's men have won just one of their seven Premier League games this season, sitting 18th in the table.
For a side who flirted with Champions League qualification for much of last season, it has been a dismal start to the campaign and Bilic needs to fix it as soon as possible.
Palace have been in decent form, however, as Alan Pardew's side sit eighth in the table after winning three and drawing two of their first seven outings.
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