(Bloomberg) -- Hedge funds have accumulated the biggest short position on junk bonds since 2008 in another sign that investors are lining up to bet against frothy debt markets.About $55 billion of global high-yield bonds has been sold short, according to data from IHS Markit Ltd. That’s up from $35 billion at the start of the year.The heady mix of rich valuations and willingness of bond bulls to throw cash at ever-riskier companies is raising alarm bells that credit markets are looking increasingly stretched. Add in the threat of rising interest rates, and there’s plenty of reason for some investors to be nervous.“I would expect that list to get bigger as spreads tighten and/or people get worried about rates rising,” said Tim Winstone, a portfolio manager at Janus Henderson, which oversees 294 billion pounds ($409 billion). “At these levels of valuations, I’m not surprised more people, such as hedge funds, are setting shorts.”In the euro-denominated investment-grade market, roughly $30 billion equivalent of bonds have been borrowed, the largest loan balance since early 2014. Bond investors including Pacific Investment Management Co. have been cutting down on broad-brush bullish bets lately, citing expensive valuations after a rally that has run for over a year.The trend is having an impact on the performance of deals in the secondary market. Almost one out of four high-yield bonds sold this year is indicated below the price it was issued at, based on data compiled by Bloomberg.The trend has been attributed to so-called fast money from hedge funds that seek to sell the debt quickly at a profit, or with an interest to short.A 275-million-euro deal by Standard Profil Automotive GmbH fell four cents on the euro just days after pricing in the primary market last week. The deal is one of the worst performers among 2021 issues, trailing only two notes from retailer Iceland and packaging group Kloeckner Pentaplast.Investors are building up defenses against a potential scaling back of central-bank support. While the Federal Reserve maintains it isn’t ready to discuss a tapering of asset purchases yet, investors bet the U.S. central bank will come under pressure to do so later this year. Meanwhile, the European Central Bank could decide to prune its emergency bond-buying program as early as next month if the euro-area economy doesn’t deteriorate.On Thursday however, the Bank of England said it doesn’t intend to tighten until there’s clear evidence of rebound. Yields on 10-year U.K. government bonds have fallen for four of the past five weeks and risk premiums in sterling company debt traded near post-financial-crisis lows.Yet, investors are also seeking to taper-proof their portfolios with the turbulence of 2013 still fresh in their minds. The Fed warned Thursday that rising appetite for risk is stretching valuations and creating vulnerabilities in the U.S. financial system.Read More: Fed Warns of Peril for Asset Prices as Investors Gorge on RiskSome say the shorting strategy is premature.Kshitij Sinha, a portfolio manager at Canada Life Investments, which oversees 41 billion pounds ($57 billion), doesn’t see scope for significant repricing yet.“Shorting cash corporate bonds just for spread widening is very expensive,” he said. “You are better off expressing that view through CDS, either in single names or indices.”EuropeEuropean credit risk is in focus after macroeconomic data from the world’s largest economies showed a recovery is well under way.Credit Agricole joined regional peers in posting a strong trading performance, as 1Q profits jumped and it booked lower-than-anticipated charges to cover potential loan lossesSome German companies also reported promising earnings numbers, with Adidas raising its 2021 sales forecast and Siemens increasing expectations for its 2021 net; BMW reaffirmed its outlook for the year and said its automotive Ebit margin will come at the upper end of its forecastThe primary credit market is expected to slow down today as the week draws to a close; Erste plans to offer an inaugural sustainability bond, while FMO could bring a USD 5Y securityMeanwhile, the European Central Bank could decide to scale back its emergency bond-buying program as early as next month if the euro-area economy doesn’t deteriorate, according to Governing Council member Martins Kazaks.AsiaIssuers from the aviation industry were in focus in Asia’s primary dollar bond market on Thursday with BOC Aviation offering 3-year notes and Cathay Pacific mandating banks for dollar debt sale which would be its first since the 1990s.The bond from BOC Aviation came after the aircraft financing company raised more than $1 billion so far this year, data compiled by Bloomberg showsAsian investment-grade dollar bond spreads widened as much as 1 basis point, traders said, as investors assessed factors including the latest pandemic setbacks. But they remain down on the year and near the lowest since early 2020Naver Corp. received over $650 million of orders for its $300 million notesU.S.EQT agreed to acquire all of the membership stake in Alta Resources Development’s upstream and midstream subsidiaries for about $2.925 billion, to be funded with cash on hand, drawings under our revolving credit facility and/or through one or more debt capital markets transactionsThe Reddit army’s meme-packed campaign to boost GameStop stock price has now resulted in one of the most conventional victories on Wall Street: a credit-rating upgradeInternational Business Machines Corp. was downgraded by S&P Global Ratings one notch to A-. The ratings firm said an acquisition spree adds doubt to the tech company’s time line for reducing debt(Updates with reference to Pimco’s positioning in fifth paragraph)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2021 Bloomberg L.P.