Tishman is one of four remaining bidders for the site, (Brookfield Properties dropped out  last week) and, until today, was one of three with an anchor tenant.
Related  has secured Newscorp and Durst-Vornado  is working with Conde Nast on their bid. Extell  is the remaining bidder with no major tenant backing going into the bidding process. While Tishman is not out of the race officially, MTA execs have made their preference for bids with anchor tenants known.
Morgan Stanley's retreat is yet another sign of the increasing trepidation among would-be investors in this mega-site. Given the uncertain future of the real estate market, it's no surprise that bidders are hesitant about this enormous investment. According to the Times,
The winning bidder will have to put up $20 million immediately and complete a final contract within four months, when it must make a $100 million down payment. The transportation authority expects that it will take 18 months after that to prepare the property for construction, and two to three years and about $1.5 billion to build platforms and foundations over the railyards.
The MTA maintains that a bidder will be chosen by the middle of March.
Morgan Stanley Retreating From Railyards Development  [New York Times]