Tesla and SpaceX could grow closer in the future and possibly even combine, says one analyst.

Tighter collaboration between Elon Musk's two largest companies could help Tesla fend off competition and access capital while allowing both companies to share resources and information and collaborate on new businesses, said Morgan Stanley analyst Adam Jonas in a note sent Tuesday.

To be sure, there are no stated plans to merge the two companies. But Musk and other Tesla executives have said SpaceX and Tesla have worked together in the past.

Strategic partnerships, shared technology, or even a combination of the two companies are ways the two companies could become more intertwined, Jonas said.

One reason it may make sense for Tesla to collaborate more or even combine with SpaceX is that it may become increasingly difficult for Tesla to continue as an independent company, Jonas said.

For example, the company could soon face stiff competition from established automakers and deep-pocketed tech firms. Large tech firms in particular will have "arguably superior access to capital, talent and business models that can monetize vehicle data and content opportunities," he said.

Tesla already has intense capital needs. Bernstein analyst Toni Sacconaghi said he expects the company to burn $4.7 billion in 2017 alone, as the company expands production on the Model 3 and invests in other businesses.

But there seems to be no "apparent natural buyer" for Tesla, Jonas said. The capital intensity of Tesla's business and other economic and political factors, such as barriers to foreign ownership, leave few likely candidates.

But a tighter relationship with SpaceX could allow the companies to share resources, and perhaps offer Tesla access to capital. SpaceX bought some of SolarCity's debt before Tesla purchased the solar power company. SpaceX's launch business appears to be in a "highly dominant position," according to Jonas' models, and the company looks well-positioned to enter "highly profitable" markets, such as proprietary satellite broadband.

Musk already divides his time between the two companies, and he may further reduce his time at Tesla to focus on SpaceX. This poses a risk for Tesla as many investors consider Musk to be essential.