FRANKFURT Dec 13 The German federal cartel office said it has reservations over a plan by hospital operator Asklepios to take a stake of up to 10.1 percent in rival Rhoen-Klinikum.
The cartel office said that due to Rhoen's structure, a stake of just 10 percent would act as a blocking minority.
Rhoen is however considering changing its bylaws, after its structure - whereby shareholders representing at least 90 percent of its stock must approve any major decision - effectively scuppered a bid by Fresenius, a company source told Reuters in November.
The cartel office will make a final decision in mid-January.
Shares in Rhoen rose were up 2.3 percent at 1356 GMT. (Reporting by Victoria Bryan)