A federal judge agreed Monday to appoint an outside lawyer to monitor CVS Health Corp.’s acquisition of Aetna Inc. but raised continued concerns about the two companies integrating their businesses while the $69 billion deal remains under his review.

U.S. District Judge Richard Leon in Washington, D.C., suggested CVS’s management should be insulated from Aetna’s while he weighs approving the companies’ settlement with the Justice Department, which cleared the acquisition on the condition the insurance giant sell off its independent prescription drug plan business.