CrowdStrike (CRWD) - Get Report shares were falling sharply in trading Monday following a bearish note from Citigroup challenging the company's valuation multiple due to market concerns. 

The firm initiated coverage of the stock with a sell rating despite noting that the digital security company is one of the fastest growing security companies in history after achieving more than $500 million in recurring revenue just eight years after its founding.

"While the trajectory is impressive, it's not unheard of in security, we view the market opportunity as not enabling a sustaining of this growth," Citi's note said. 

Citi set a $43 price target on the stock, a potential 29% downside from the stock's closing price Friday of $60.27. 

This is the second downgrade CrowdStrike has experienced in the past two trading sessions. Analysts at Goldman Sachs turned bearish on the company Friday, downgrading the stock to sell from neutral while also cutting their price target to $66 from $83. 

"The stock has gained 85% since its June IPO vs. the S&P 500 at 1% over the same time period, and while we continue to see room for considerable revenue outperformance, we believe the shares are factoring in this outcome," Goldman Sachs analyst Heather Bellini said. 

CrowdStrike shares were falling 8.3% to $55.28 in trading Monday.