Jawbone, the buzzy but financially strapped maker of Up fitness bands and Jambox speakers, is close to receiving a major investment from BlackRock BLK , the world’s largest asset manager. According to sources, BlackRock is considering investing as much as $300 million.

The San Francisco company has raised more than $400 million during its 16-year, roller-coaster existence, but its financial position has become increasingly tenuous as it has missed production deadlines and fallen behind in the markets it helped create.

Re/Code recently said Google GOOG is considering a “strategic investment” in Jawbone, but Fortune‘s sources say Google isn’t actively considering such a move.

Neither Jawbone nor BlackRock would confirm details of the transaction, which isn’t complete and could yet fall through. Jawbone also is talking to other financial institutions. But sources close to both parties confirm the two are in advanced talks for the investment, which would constitute an eleventh-hour lifeline for Jawbone.

The company’s signature product, the Up3 fitness-tracker bracelet that includes a heart-rate monitor, has been delayed for months. Last year, Jawbone also settled a breach-of-contract lawsuit with Flextronics FLEX , its previous contract manufacturer, which had sued to recover $20 million in delinquent payments. According to sources, Jawbone has since defaulted on a payment plan set up to satisfy the debt, which last stood at $16 million. Jawbone denied it is in arrears on its payments to Flextronics, which didn’t comment on the matter.

As it tries to raise funding to shore up its finances, Jawbone also is making changes to its star-studded board of directors. Former CEO and co-founder Alexander Asseily will relinquish his position as chairman. It isn’t clear who will replace him, but candidates would include Jawbone’s investors and current directors—including venture capitalists Ben Horowitz, Vinod Khosla, and Mary Meeker—all of whom have been actively advising Jawbone during its hour of need.

Jawbone is a unique company in the lore of recent Silicon Valley history. (See “The trials of a 16-year-old can’t-miss startup” from the February 2015 issue of Fortune.) It grew out of research conducted in noise-canceling technology at Stanford University in the late 1990s and struggled as a small outfit until 2007, when its Aliph wireless headset took off. The company’s co-founder, Hosain Rahman, by that time had become CEO and teamed up with designer Yves Béhar, who has continued to work as a part-time executive for the company. Jawbone’s wireless speaker, the Jambox, created a new category in consumer electronics, but failed to maintain a leading market share. Similarly, Jawbone helped popularize the “wearables” market but has ceded the leading position to crosstown rival Fitbit.

Jawbone has had trouble raising money for the past year, coinciding with its challenges to release its latest product. On Nov. 5 last year the company began taking pre-orders for the Up3, saying the product would be available “by the end of the year.” On Dec. 11, Rahman told Andrew Ross Sorkin of The New York Times in an onstage interview that the fitness tracker would ship “soon.” Instead, a week later, Jawbone announced the Up3 would be available “early next year” and that customers who pre-ordered would receive a $40 discount on the $180 device. The company’s website currently says new orders will take 10 to 11 weeks to fulfill, pegging the device’s arrival well after the release of the much-anticipated Apple Watch. Apple AAPL has said it plans to ship the product in April, and on Thursday it announced that it will hold an event March 9, presumably to unveil the watch.

A source close to Jawbone suggests the company is days away from announcing a more specific timeline for releasing the Up3. It likely is waiting to secure the funding, which would be critical to financing the manufacturing and shipping of its product. Rumors have persisted for months that Jawbone has had trouble paying its bills. A rumor even went around the company’s San Francisco headquarters that there was no milk in its kitchens because the company hadn’t paid its dairy vendor. As with the other more substantive information under discussion, a Jawbone spokesman declined to comment.