Shares in Gemstar-TV Guide International Inc. plunged nearly 20 percent Monday after an analyst speculated that Macrovision Corp.’s acquisition of the company may be jeopardy.

Moody’s Investors Service lowered Macrovision’s senior secured debt ratings on Friday, citing a change in the company’s capital structure. Kaufman Brothers analyst Todd Mitchell said that the Macrovision downgrade “creates the perception the deal’s in question.”

Macrovision agreed to buy Los Angeles-based Gemstar for $2.8 billion in cash and stock last year. The deal is expected to close early in the second quarter.

Shares in Gemstar were down 18 percent to $4.23 in early trading Monday.