In a regulatory filing, the company said Hollis' resignation "was due to personal reasons and not because of a disagreement on any matter relating to Diamondback's operations, policies or practices."
The stock was down $2.10 to $87.81 on Tuesday.
RBC's Scott Hanold, who has an outperform on the stock and $156 price target, according to Bloomberg, wrote in a note that the move was a surprise.
Bloomberg also reported that Susquehanna analyst Biju Perincheril lowered the company's third-quarter oil production estimates and cut the price target to $125 from $130.
Perincheril doesn't see the third-quarter weakness as an indication of a longer-term trend, but noted there could be headwinds for shares.
FANG has 38 buys and no holds or sells with an average price target of $143, according to Bloomberg.
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