The Federal Trade Commission signaled concern Friday over the potential anti-competitive effects of a proposed merger between DaVita Inc. and Gambro Healthcare, requesting more information about the deal.

The effect of the request, the second by the agency, will be to delay the completion of the $3.4 billion acquisition until 30 days after a response. The deal would create the nation’s largest chain of dialysis centers.

DaVita said it would respond promptly to the FTC’s request.

The move by the FTC appeared to be anticipated by Wachovia Capital Markets on Thursday, when it cut DaVita’s rating to “market perform” from “outperform” citing concerns the deal might be dilutive and DaVita may be forced to make divestitures to complete the transaction.

Morgan Stanley on Thursday also lowered its investment rating on DaVita to “equal weight” from “overweight,” citing that the stock had appreciated 50 percent since August, nearly reaching its price target.

DaVita shares dropped 41 cents to $41.84 in afternoon trading.