The US real estate investment group had an initial approach rejected back in May and told the market it would “actively” consider coming back with a new offer.
It has decided not to return with an improved bid though and gave no explanation why.
FTSE-250 IWG issued a profit warning at the end of June, claiming its UK business is “not performing to management expectations”.
Despite Prime Opportunities pulling out of the race, private equity firms TDR Capital and Terra Firma, along with real estate investor Starwood Capital are all reportedly interested in buying the Regus owner.
Shares were broadly flat at 302.6p in early deals on Monday.