Fears are growing that more than 2,000 staff could lose their jobs if music giants EMI and Warner Music merge.
EMI had a $4.3bn (£2.3bn) bid for its US rival rebuffed earlier this month and is expected to make a higher offer soon.
But an EMI shareholder said this weekend that chairman Eric Nicoli had not convinced them that his company should take over Warner Music, rather than be swallowed up itself by the American-based firm.
Shareholders and analysts will quiz Mr Nicoli about his plans this week when EMI reports annual results.
Warner Music, whose artists include Madonna and James Blunt, is thought to be considering a counterbid for EMI. The two companies have been sporadically trying to merge since 2000. Schroders, which owns around 2.3 per cent of EMI, has already voiced objections over the company's plans for a rights issue to help fund the bid.
Now another shareholder, who declined to be named but owns around 1 per cent of the company, said EMI's management had not put a convincing case forward about its merger plans. "The question is whether EMI can convince us that they are the right ones to run the combined company, given how well Warner Music has done. We would need reassurances from EMI. They have to put a good case forward."
Around 75 per cent of Warner Music is owned by private equity groups, after their buyout of the company from its former owner, Time Warner.
EMI, which includes Gorillaz on its roster of artists, announced plans last month to cut costs by £30m each year, but Warner Music still has one of the highest productivity levels in the industry per employee following cost-cutting.
Simon Wallis from stockbrokers Collins Stewart estimates savings of between £160m and £230m a year could be made if the two companies merge. Around £50m could be saved by merging headquarters and cutting back office staff, such as accountants and lawyers, he said. The rest would come from a reduction in operating costs.
Mr Wallis estimated a fifth of the combined workforce of about 10,600 could lose their jobs. Warner Music employs 4,000 staff, and EMIhas around 6,600 on the payroll.
A spokesman for broadcasting union Bectu said if the companies merged, job cuts of 20 per cent would be "optimistic".
Staff in the UK include around 80 at EMI's Abbey Road studios in north-west London, made famous by The Beatles. The music giant's headquarters are in Kensington, west London, where several hundred are employed.