The premarket drop in Grifols' shares is a direct reaction to the short-seller report from Gotham City Research. Short-seller reports typically contain allegations of operational or financial misconduct, which can lead to a loss of investor confidence and a sharp decline in stock price. The 35% drop indicates a significant negative impact on the stock, suggesting that the market is taking the contents of the report seriously. However, without details on the specific allegations, the long-term impact remains uncertain.