In June, Rupert Murdoch's News Corp failed in a 700p per share bid to buy the 61% of Sky that it does not already own. However, the two parties agreed to keep the lines of negotiation open.
Writing in a comment piece in The Guardian, Lord Fowler said that the takeover endangers plurality in the British media as News Corp already owns several major newspapers, such as The Times and The Sun.
Lord Fowler, the former chairman of the House of Lords select communications committee, said that the biggest concern is the loss of control for Sky's board of independent directors.
"The directors have a duty and responsibility to the other shareholders, who own 60% of the company - and by all reports show a commendable independence of judgment. It is not some cosy little advisory board that meets infrequently and has next to no influence," he said.
"If News Corp takes full control, that represents real change and an increase in real power. It reduces the plurality of media ownership which should be a prerequisite in a thriving democracy."
Last week, BBC director general Mark Thompson warned of the potential for "abuse of power" should News Corp be allowed to take full control of Sky.
Lord Fowler noted that opposition to News Corp's takeover comes from "rivals who are not always acting altruistically", or are willing to subject themselves to "public scrutiny".
He said that the BBC "needs to be careful before fulminating too much about media power" as it has a near monopoly on news radio, while the daily political agenda is "set not by Parliament but by the Today programme".
The position will only get worse, he said, if ITV withdraws its regional news services, leaving the BBC in "almost total command".
However, Lord Fowler stressed that concerns such as these should not dissuade Cable from exerting his power to block News Corp from taking full control of Sky and its £6bn annual revenues.
"Any proposal to allow a company of that size to come under the same ownership as the country's largest national newspaper group must be a matter of legitimate public concern," he said.
"So Cable should certainly call in any bid by News Corp for full control of Sky - but that should not be the end of it. The government should go one step further and examine what impact the increasing concentration of ownership is having on the news we all receive."
In the next fortnight, News Corp is expected to formally notify the European Commission about its intention to mount a bid for Sky. That will kick off a regulatory process that could result in Cable referring the deal to media regulator Ofcom for further investigation.