Standard Life, one of Royal Dutch Shell's key investors, has said it will oppose the oil giants proposed takeover of BG Group.
The investment firm's head of equities said that oil prices are not high enough to warrant a deal. Brent crude oil is currently trading at around $33 per barrel, having fallen from around $110 less than two years ago.
David Cumming said that for a takeover to work in Shell's favour, oil prices needed to be around $60 per barrel.
Shell shareholders are due to vote on the proposed £47 billion takeover later this month. But Standard Life will vote against the move, Mr Cumming said.
Speaking to the BBC, Mr Cumming said: "The problem we have with the deal is that a lot's changed since the bid was announced in April last year - all of it negative.
"The current oil price is $33 and Shell still needs an oil price well over $60 to make it work financially."
Despite the fund manager's opposition, Shell is still confident that the takeover will be approved. A spokesperson said: "We continue to believe we have the broad base of shareholder support we need for the deal to complete."