By Julie Steinberg and Duncan Mavin

LONDON -- Executives at Credit Suisse AG are reviewing several of the bank's funds after becoming concerned about the multiple roles played by Japanese conglomerate SoftBank Group Corp., according to people familiar with the matter.

Four Credit Suisse funds have $7.5 billion in assets in total and are sold to institutional investors and wealthy families as safe, short-term investments. They hold securities backed by loans made to companies to allow them to pay their suppliers more quickly.

SoftBank plays three roles in the Credit Suisse funds: it is invested in the funds; it is invested in the company whose loans are held by the funds; and the funds own securities backed by loans made to other companies that SoftBank has invested in.

The review was launched after senior executives at the bank became concerned about SoftBank's roles in the funds, one of the people familiar with the matter said. But it is wide-ranging, and includes other aspects of the funds not related to SoftBank.

The company tying this together is Greensill Capital, which offers supply-chain financing to companies, a form of short-term cash that lets them pay their bills more quickly. Greensill, founded in 2011 by former Citigroup Inc. banker Lex Greensill, counts former U.K. Prime Minister David Cameron as an adviser. It is the sole supplier of the supply chain finance deals that go into the Credit Suisse funds.

A Credit Suisse spokesman pointed to a statement he made earlier this week confirming the review. A Greensill spokesman said the firm isn't involved with Credit Suisse's internal matters and that it has a strong relationship with the bank.

A SoftBank spokeswoman declined to comment.

David Erickson, a senior fellow in finance at the University of Pennsylvania's Wharton School, said there should be guardrails to protect investors from potential conflicts of interest, such as disclosures about SoftBank's role as an investor in the fund and its relationship to Greensill and companies that the fund finances.

In essence, SoftBank serves as both a lender and borrower in the transactions. The fund documents reviewed by The Wall Street Journal don't disclose SoftBank's connection to Greensill or to the companies receiving financing, though there is no requirement to make such a disclosure.

Last year, the Vision Fund made a nearly $1.5 billion investment in Greensill through two tranches that valued the company at $3.5 billion. SoftBank currently has a 9.9% equity stake in the company, according to a document viewed by The Wall Street Journal and people familiar with the investment.

The rest of its stake was structured as a convertible bond, because SoftBank would have needed approval for a larger equity stake from regulators in Germany where Greensill owns a bank.

The SoftBank relationship with Credit Suisse deepened in recent months as one of the funds bought securities backed by loans made to other Vision Fund portfolio companies. Four such companies were among the top 10 recipients of financing from the fund, receiving about $750 million in aggregate as of March 31, according to a fund document.

SoftBank was struggling even before the coronavirus slowdown, with several of its companies -- including office-space provider WeWork -- falling in value. Most of the company's investments are in money-losing young companies in fast-growing industries.

The four Vision Fund companies are auto-financing company Fair Financial Corp.; Indian hotel chain Oyo Hotels & Homes; glass manufacturer View Inc.; and Chinese online car-trading platform Chehaoduo Group.

Fair's chief executive stepped down in October following layoffs at the company. Oyo announced thousands of layoffs in January and its chief executive in April said its "balance sheet runway has come under severe stress" due to the pandemic.

SoftBank also injected $500 million into the Credit Suisse funds, according to the person familiar with the matter. It isn't clear when the investment was made.

The Credit Suisse funds boomed last year, more than quadrupling assets under management to more than $9 billion from about $2 billion as clients including corporate treasurers, pension funds and family offices poured in money.

This year the funds were hit by a wave of redemptions amid the economic turmoil, though flows have stabilized in recent weeks.

The Credit Suisse funds resemble money-market funds that hold commercial paper, which are short-term loans to companies. The funds provide financing to blue-chip companies such as Kellogg Co. and General Mills Inc., as well as lesser-known firms, such as the SoftBank-backed startups.

Investors view these funds as a safe way to boost returns. The risk is if investors fear they will lose money, they will sell out of the funds, potentially creating a liquidity squeeze similar to a run on a bank.

Some clients of the funds that have each received tens of millions of dollars in financing have recently run into financial difficulties. They include NMC Health PLC, U.K.-based rent-to-own business BrightHouse Ltd. and Singapore commodities trader Agritrade Resources Ltd., which have all filed for restructuring.

The Credit Suisse review is the second time in recent weeks that a SoftBank investment in a European financial firm has come under scrutiny. An affiliate of SoftBank, backed by SoftBank executives, helped arrange EUR900 million ($1.01 billion) worth of convertible bonds in German fintech company Wirecard AG, a payments processor which filed for insolvency Thursday. The convertible bonds were later packaged up and resold by Credit Suisse to third-party investors.

Marketing documents for the Credit Suisse funds say the bank's portfolio managers operating the fund don't "exercise full discretionary investment management duties in respect" of the investments. People familiar with the funds say the portfolio managers can decide to reject the notes brokered by Greensill, though they have only done that on a few occasions.

"Properly underwritten trade credit is a steady, reliable and uncorrelated investment," said an investment manager who invests in private credit including trade finance. But products whose main assets come through a single broker dealer, like in Greensill's case, are atypical, he said.

Write to Julie Steinberg at julie.steinberg@wsj.com and Duncan Mavin at duncan.mavin@wsj.com