Cramer: The auto debt growth in the US is worth monitoring

GM November US sales up 10.2% vs. 8.4% est.

CNBC's Jim Cramer said on Thursday to keep an eye out on the number of subprime delinquencies after New York Fed researchers said millions of Americans are falling behind on their car loans.

The number of subprime auto loans falling into delinquency hit its highest level in six years, The Wall Street Journal reported Wednesday, and the rise has caused concern for U.S. regulators.

"Even though the balances of subprime loans are somewhat smaller on average, the increased level of distress associated with subprime loan delinquencies is of significant concern, and likely to have ongoing consequences for affected households," Fed researchers wrote in a post Wednesday.

Cramer said the new data is something worth monitoring.

"The subprime stuff — I don't know," Cramer said on "Squawk on the Street." "When you talk to bankers behind the scenes, they continue to say, look, you need your car to go to work. And it's not going to be like a house where you leave the keys. We've heard it before."

The Fed's remarks on car loans comes as Ford posted Thursday better-than-expected sales in November. Cramer said the report comes as a surprise to some analysts who were expecting much weaker numbers.

"This is a remarkable number for Ford," Cramer said. "A lot of people felt November would be a weaker month because some of the retail numbers. That F-150 a lot of people were concerned that had been peaking."