A growing number of money managers are embracing a new strategy designed to benefit from volatility in junk-rated corporate loans, a sign of building worries about riskier borrowers and the market that supports them.

Since November of last year, three different money managers have issued $1.6 billion of so-called enhanced collateralized loan obligations that are set up to hold a much larger amount of loans with extremely low credit ratings than typical CLOs. At least two more managers are expected to follow suit in the coming...