Japan was expecting the U.S. to return to the Trans-Pacific Partnership (TPP) fold and was only "pretending" to negotiate a bilateral deal, Kotaro Tamura, a Milken Institute Asia Fellow, told CNBC on Tuesday.

"Japan's prime minister and government paid a tremendous amount of political capital to make [the TPP] happen. They won't waste it," said Tamura, who was a Japanese senator from Prime Minister Shinzo Abe's Liberal Democratic Party (LDP) from 2002-2010.

"Of course they were pretending to talk about a free trade agreement (FTA), but bottom in the heart, they will be welcoming the U.S. back," he told CNBC's "The Rundown" on Tuesday. "It's not about FTA. It's buying time, but in reality, they are looking for the U.S. coming back to the pact."

Abe reiterated in an interview with CNBC on Monday that Japan would continue to push for an ex-U.S. TPP deal.

U.S. President Donald Trump pulled the U.S. out of the TPP, a broad 12-nation trade deal, which he claimed was a "disaster" that would hurt U.S. manufacturing.

Japan's prime minister had initially said that the TPP would be "meaningless" without the U.S., but more recently, Japanese officials have seconded Australia's calls for the other 11 members of the pact to proceed without the U.S.

Trump has expressed a preference for bilateral trade agreements, over multi-lateral ones, claiming he can negotiate better deals that way.