Analysts at MoffettNathanson do not think Time Warner will save AT&T.

On Tuesday, a federal judge ruled that the deal, which would give AT&T ownership of cable channels like CNN and HBO as well as the film studio Warner Bros., was legal without any conditions.

Analyst Craig Moffett said in a research note Wednesday that his firm was downgrading AT&T stock from a neutral rating to sell and lowering its price target to $28 a share from $35 to account for the Time Warner acquisition.

"Time Warner will be a positive for AT&T's income statement, at least initially. But it will be a negative for the balance sheet," Moffett wrote, adding that the combined company will carry $249 billion in debt, inclusive of operating leases and postretirement obligations. "We believe that there will be continued erosion in each of AT&T's legacy businesses as the company doubles down on bundling (discounting)."

Given the pressures in AT&T's legacy satellite, broadband and wireless businesses and the impact to the company's debt ratios, "AT&T will be under enormous pressure from the credit rating agencies to de-lever," he said.

That raises the question of whether AT&T's dividend is safe, he wrote.

AT&T shares were down nearly 5 percent Wednesday to $32.72.