Fitch Ratings has downgraded TCF Financial Corp.’s primary bank rating to BBB- from BBB, citing weak asset quality and reliance on the consumer market.

The downgrade, issued late Thursday, is for the bank’s long-term issuer default rating — the main rating covering the entire company and all of its debt. Fitch also downgraded the bank’s short-term debt rating to BBB-.

The downgrade, with a negative outlook, puts TCF a notch above “junk” status. BBB- is the lowest investment-grade rating. Lower ratings make it more expensive for companies to borrow money or issue debt and are likely to make a bank more dependent on deposits for funding.

It’s the lowest grade Fitch has given the bank since 2000.

A TCF spokesman said the bank had no comment.

Fitch said in its notice that the downgrade “primarily reflects the company’s sustained weak asset quality and consumer-oriented, higher-risk balance sheet compared to other mid-tier regional banks.”

“Fitch remains concerned about the company’s level of exposure to consumer real estate relative to capital that has been thinned out through strategic balance sheet restructurings as well as the relatively lower level of readily available liquidity on balance sheet.”

The downgrade followed a peer review that Fitch conducted of 16 mid-tier regional banks, which are banks with assets between $10 billion and $36 billion. TCF was one of three banks downgraded; the others were Fulton Financial Corp. based in Lancaster, Pa., and UMB Financial Corp. in Kansas City, Mo.

As a group, the mid-tier banks are more heavily reliant on what they make on loans and investments, Fitch said.

“With limited opportunity to improve fee-based income in the near term, Fitch expects that mid-tier banks will continue to face greater earnings headwinds in 2013 than larger institutions with greater revenue diversification.”

Jon Arfstrom, bank analyst with RBC Capital Markets in Minneapolis, wouldn’t comment on the downgrade. But he noted that TCF is not a heavy debt issuer, and that his perception is that TCF’s asset quality is improving.

“Consumer credit has shown steady improvement over the last few quarters,” he said.