Tesla Inc. shares fell after Chief Executive Elon Musk signaled he was open to selling 10% of his holdings.

Shares in the electric-vehicle maker lost 4.8% Monday after Mr. Musk, the company’s largest stockholder, launched a weekend poll of his 63 million followers on Twitter , asking them if he should sell the stake, worth around $21 billion at Friday’s market close, to pay taxes. About 58% of the 3.5 million participants voted in favor of the sale and Mr. Musk tweeted that he had been “prepared to accept either outcome.”