What happened

Shares of electric-truck start-up Nikola (NASDAQ:NKLA) opened sharply lower on Wednesday, on growing concerns about potential insider sales when a lockup period expires next week, and on continuing questions about the status of the company's partnership with General Motors (NYSE:GM).

As of 10:30 a.m. EST, Nikola's shares were down about 13.7% from Tuesday's closing price.

So what

Appearing on CNBC's Mad Money program on Tuesday evening, CEO Mark Russell said that while Nikola remains interested in GM's electric-vehicle batteries and hydrogen fuel cells, the companies have yet to close a deal. Russell confirmed that Nikola's discussions with GM are still ongoing, but said that he couldn't comment on the state of those discussions.

Nikola and GM announced in September that GM would supply batteries and fuel cells for Nikola's electric trucks, and develop and build Nikola's electric Badger pickup, in exchange for a $2 billion stake in Nikola. But the deal -- or at least, the valuation of the stock included in GM's stake -- was thrown into question after a short-seller's allegations tanked Nikola's stock and led to the departure of founder Trevor Milton.

A silver Nikola Badger, an electric pickup.

A revamped Nikola-GM deal might or might not include the start-up's Badger pickup truck. Image source: Nikola.

Nikola's stock jumped on Tuesday after GM withdrew from a Trump administration suit seeking to void California's fuel-economy standards, which are stricter than the federal government's. That development, along with the accelerated electric-vehicle efforts that GM announced last week, seemed to suggest (to some investors, at least) that a deal with Nikola might be imminent.

Russell's comments suggested that things are still up in the air. 

Now what 

There's another concern on investors' minds: About 161 million Nikola shares held by insiders that have been "locked up" since the company went public in June will be "unlocked" as of next Tuesday, Dec. 1. Of note, and of particular concern to auto investors: Milton holds 96.1 million of those shares, and it's not clear whether he plans to hold them indefinitely. 

If you own Nikola because you like the long-term potential, there's no sudden reason to sell. But be prepared for the likelihood that the stock will be quite volatile over the next couple of weeks.