Shares of both CBS (CBS - Get Report) and Viacom (VIAB - Get Report) traded sharply lower on Wednesday, a day after the media giants formally revealed their $30 billion tie-up, after an influential analyst at Bernstein downgraded CBS and cut his 12-month price target.

In a research note to clients, Bernstein analyst Todd Juenger downgraded CBS to underperform from outperform and slashed his price target to $46 from $62 on concern that CBS will lose more from inheriting Viacom's structural problems than it will gain from any synergies.

"What a shame," Juenger said of the deal, using the phrase as the title of his note. "We believe whatever synergies are produced (we assume $750 million) will pale in comparison to CBS shareholders investing in Viacom's structural problems."

CBS and Viacom agreed on Tuesday to combine in a long-awaited all-stock merger, creating a combined company with more than $28 billion in revenue and a market capitalization of about $30 billion.

The two media companies, which had been part of one company run by media mogul Sumner Redstone until 2006, will recombine as a new entity known as "ViacomCBS Inc."

Shares of CBS were down 7.6% to $45 in trading on Wednesday, while shares of Viacom were down 7.81% to $26.93.

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