Former Normandy Real Estate Partners executive Justin Krebs is teaming up with developer Steve Belkin to bolster Belkin’s attempts to build a 740-foot-tall skyscraper in downtown Boston.

Krebs has joined Belkin’s Trans National Properties as executive vice president, Belkin announced Monday. He will be in charge of Trans National’s selection of a co-developer.

Belkin last fall publicly floated a proposal to acquire the city-owned site at 115 Federal St. for a $900-million mixed-use development, including office space, a luxury hotel, residential units and ground-floor retail.

Belkin’s proposal is expected to be just one of several for the site which contains a four-story, 1,125-space parking garage that was closed in May 2013 due to its deteriorating condition.

In February, the Boston Redevelopment Authority issued a request for interest for developers for the one-acre parcel. The proposals are due April 13.

Krebs left Normandy in December after most recently serving as partner in charge of its Boston office. At Normandy, Krebs oversaw management and leasing of the John Hancock Tower and was involved with permitting for the new TripAdvisors headquarters in Needham and the 378-unit Troy residential project in Boston’s South End.

Belkin, a former owner of the NBA’s Atlanta Hawks and founder of travel company Trans National Group, proposed a 1,000-foot tower on the same site prior to the recession. Trans National owns 133 Federal St., an abutting property that contains a 12-story office building.