The UK’s Competition and Markets Authority (CMA) is looking into whether AstraZeneca’s proposed $39 billion buyout of Boston, Mass.-based Alexion Pharmaceuticals would stifle competition.

The antitrust regulator said it will decide by July 21 whether the deal warrants a more thorough probe. An extended review is considered unlikely, but in certain cases they can last up to 32 weeks.

The review is “another important step toward closing of the proposed acquisition, which we continue to expect will be in [the third quarter of] 2021,” an AstraZeneca spokesperson told FDAnews.

In December, AstraZeneca announced plans to acquire Alexion in a move to significantly expand its rare disease immunology portfolio. The deal, which has already been cleared in the U.S. by the Federal Trade Commission, would give the Anglo-Swedish drugmaker access to Alexion’s novel immunology drugs Soliris (eculizumab) and Ultomiris (ravulizumab).