Bond issuers got a reminder last week that investor sentiment can turn on a dime and a liquid market should never be taken for granted.

Over the first two weeks of the year, companies rushed to issue debt, borrowing at their lowest rates since before the financial crisis. But there were a number of signs last week that investor appetite might finally be cooling, which could require issuers to make price concessions on new issues, according to an article in the Financial Times on Sunday.

The FT pointed to the poor performance of issuances by household names like BMW and Vodafone in secondary trading and an offering from British football club Manchester United pricing at the high end of the expected range, as well as Energy Transfer Equity pulling a $1.75 billion high-yield offering due to market conditions.

Overall, global bond sales fell 52 percent last week to $48 billion, compared to a week earlier, according to Bloomberg .

The extra interest investors demand to own corporate bonds widened 3 basis points last week to 164 basis points, Bloomberg said. That's significant considering the spread shrank almost 30 basis points over the previous six weeks.

For borrowers looking to issue debt in the future, the FT said bankers are warning that new issue premiums -- where deals are offered with slightly higher yields than existing bonds -- may be reintroduced. The high level of investor demand that kicked off the year largely wiped out such premiums.

"Issuers [are] looking to squeeze every last basis point [but] it's time to get sensible again and re-instigate new issue premiums," Suki Mann, head of credit strategy at Société Générale, told the FT.

It's unclear if the market has truly shifted or if it is a short-term reaction to negative news last week related to China reining in bank lending, Greece nearing default and a rather unspectacular start to the current earnings season.

Some market participants believe fundamentals remain strong and a big swing in pricing is unlikely.

"The technicals in the credit market are still positive: balance sheets are strong, liquidity is good, the markets are open and there's a lot of new money looking for good assets and good stories," said Jason Quinn, the co-head of high-grade and high-yield flow trading at Barclays Capital, according to Bloomberg. "The market has deleveraged substantially, so the probability that we get a massive re-pricing is low."