Another housing bubble could easily occur, says Robert Shiller, the Yale economist and co-founder of the Case-Shiller housing price index.

There is “absolutely” the possibility that the housing market could see another bubble because the affordability of homes is at a 40-year high, Shiller told CNBC.

“The low interest rates, the affordability is leaning that way and the ratios are back down,” Shiller said in the CNBC interview.

“I get glimmers of excitement among some people, but we still have a high inventory of unsold homes, we still have a lot of weariness because of the recent experience. So, I would say well under half probability that we emerge into another housing bubble in the next five years.”

Shiller said he is concerned that the recovery in the US will be “exceptionally weak.”

The government needs to be prepared to conduct more stimulus programs and support the credit markets to boost the economy.

“It’s not clearly over yet,” he said.

The latest retail numbers demonstrate that people are hesitant about buying items, Shiller said.

“It’s not obvious people are really ready to spend again,” he said.

Joe Robson, the chairman of the National Association of Home Builders, said builder confidence was boosted by the first-time home buyer tax credit of $8,000, which ends in three months.

“The question is what happens after that — whether there will be enough momentum to keep us moving toward a recovery, particularly in light of such headwinds as the severe credit crunch for housing production loans and inappropriate appraisal practices that are scuttling a quarter of all new home sales,” he said.