Softbank's pending control of Sprint's purse strings could be bad news for Clearwire's ability to tap its largest shareholder for cash.

Sprint has been a frequent source of capital for the perennially cash-poor WiMAX operator, having invested billions to fund Clearwire and gain access to its mobile broadband network. 

Clearwire disclosed in its quarterly report on Friday that Sprint must receive clearance from Softbank before making significant investments.

"Pending the closing of the transaction, Sprint is not permitted to make equity investments of more than $100 million or agree to amend material agreements without the approval of Softbank," Clearwire said. "After the transaction has closed, Softbank would likely need to approve any significant funding of Clearwire by Sprint."

The disclosure came one day after Clearwire said it would slash the number of TD-LTE cell sites it plans to launch by next summer. It will now install just 2,000 TD-LTE base stations, less than half its previous plans to roll out the equipment at 5,000 sites.

The delay will reduce Clearwire's expenses and "better align CapEx with the expected receipt of LTE revenues" from Sprint, a key wholesale customer for the new service. 

Sprint has agreed to advance Clearwire $350 million for the use of its TD-LTE network if the operator meets buildout milestones. Clearwire executives have said its reduced deployment plans will not affect the prepayment amount.

The loss of the Sprint cash cow could force Clearwire to find different funding sources, such as selling off its formidable spectrum assets, because "additional debt financings may not be available on acceptable terms or at all and, even if available, could increase our future financial commitments, including aggregate interest payments on our existing and new indebtedness, to levels that we find unsustainable," Clearwire said.

The company said its $1.18 billion in cash and short-term investments is enough to last the next 12 months, but warned it will need more funding to run its business after that time expires. 

"We will need to raise substantial additional capital to fund our business and meet our financial obligations beyond the next 12 months," it said. Unforeseen expenses could also push up its need for cash.

Clearwire has long said it may opt to sell off some of its "excess" spectrum, but has yet to announce a buyer. 

Its funding position was not the only interesting item in Clearwire's quarterly report. It also said it would use Huawei gear in a "limited" portion of its LTE network, a potentially controversial decision given that the Chinese vendor was recently labeled by the U.S. government as a cybersecurity threat. 

"Even though our planned use of Huawei in our LTE network is limited, potential wholesale partners or others could object," Clearwire said. "In such case, we may decide to incur the cost, which may be significant, of switching to another vendor."