Top investor Sass buys Allergan after epic plunge

Allergan
Scott Eisen | Bloomberg | Getty Images

Hedge fund manager Martin Sass doubled down on Allergan on Tuesday, adding to shares of the specialty-pharmaceutical company for his CNBC Pro model portfolio after the stock plunged.

In early trading, shares of Allergan lost nearly a fifth of their value at one point as the Treasury Department took steps to curb so-called tax inversions. Pfizer plans to buy Ireland-based Allergan to reduce its tax bill, and that deal is now in question.

Sass, who oversees $7 billion in assets at M.D. Sass, a New York-based firm he founded in 1972, used the remaining amount of cash in his CNBC contest portfolio to buy more Allergan stock.

Why did he do it and what advice does he have for regular investors faced with a similar situation?