Vanguard, along with Hartford Funds, pushed its estimates of the value of an Uber share down by 15 percent to $41.46 a share for the quarter ended June 30, according to disclosures by the companies. The Principal Financial Group slashed its estimate for Uber to $42.72 a share in July, down 12.4 percent from $48.77 a share in April. And T. Rowe Price is now pegging the price of its Uber shares at $42.70 each, down 12 percent from its previous estimate.

Fidelity Investments, another giant mutual fund firm, held its Uber estimate steady at $48.77 a share as of June 30.

Michael Ramsey, an analyst with Gartner, said the lower valuations by some of the mutual fund companies were most likely a proactive accounting strategy for the funds that signaled an internal dialing down of their confidence in the San Francisco-based start-up.

“They have to take a hit on their finances now to do it,” he said of the mutual funds, “but with all of the drama around Uber and its growth trajectory and leadership shake-up right now, there are a lot more signs out there that their valuation may be too high rather than too low.”

Uber is currently valued at around $68.5 billion, making it the most highly valued private start-up in the world. The company has raised more than $10 billion in debt and equity, and it holds more than $6.6 billion in cash, down from $7.2 billion at the end of the first quarter.

Because the firm is private, mutual fund companies must guess at how much their shares are worth. The markdowns were first reported by The Wall Street Journal. The mutual fund companies declined to comment on individual company valuations.

There may soon be more clarity on what exactly Uber is worth. This month, the company’s board voted to advance preliminary proposals by two investment groups — the Japanese conglomerate SoftBank and the Dragoneer Investment Group — to buy shares in the company. The board is also considering an offer from a consortium led by Shervin Pishevar, an early Uber investor, to buy shares.

While the proposals include measures that would maintain, at least on paper, Uber’s $68.5 billion valuation, the investment groups would potentially gain some of the company’s shares at a discount. Whatever that discount may amount to is likely to be heavily scrutinized.