Bristol-Myers Squibb’s planned $74-billion purchase of Celgene has hit a significant obstacle after its largest institutional shareholder said it did not back the deal.

Wellington Management, which owns around 8% of BMS’ stock, has issued a statement that it is “not supportive of the company’s proposed acquisition of Celgene”.

While Wellington agrees that BMS should be active in business development that secures differentiated science and broadens the future revenue base, it “does not believe that the Celgene transaction is an attractive path towards accomplishing this goal”.

According to the investor, the transaction asks BMS shareholders “to accept too much risk” and the terms offer BMS shares to Celgene shareholders at a price “well below implied asset value”.

It also argues “alternative paths to create value for BMY shareholders could be more attractive”.

BMS announced its intent to buy Celgene early January.

“Together with Celgene, we are creating an innovative biopharma leader, with leading franchises and a deep and broad pipeline that will drive sustainable growth and deliver new options for patients across a range of serious diseases,” said Giovanni Caforio, the drug giant’s chairman and chief executive.

“As a combined entity, we will enhance our leadership positions across our portfolio, including in cancer and immunology and inflammation. We will also benefit from an expanded early- and late-stage pipeline that includes six expected near-term product launches. Together, our pipeline holds significant promise for patients, allowing us to accelerate new options through a broader range of cutting-edge technologies and discovery platforms.”

According to media reports, analysts at Baird Research continue to believe the deal the deal “makes sense for Bristol-Myers, and ultimately will go through, despite this new risk,” but also acknowledged that Wellington “has a much more commanding position than anyone else who has taken a stance against the deal so far."