It added that any deal would rely heavily on outside capital, noting Sodastream had a negative free cash flow in each of the past three years. Stifel maintained its "sell" recommendation on the company.
Read MoreSodastream reportedly in talks to go private
Bloomberg reported on Thursday that the maker of home soda machines was in talks with an investment firm to go private, citing sources familiar with the matter. The deal would value Sodastream at $40 a share, or $828 million, a 38 percent premium above Wednesday's close.
After being halted briefly on the Nasdaq, Sodastream shares hovered more than 10 percent higher on Thursday.
Read MoreSodastream trader makes 3,000% profit in 2 hour
— By CNBC staff