LONDON (Reuters)—Aviva P.L.C., Britain's second biggest insurer, on Thursday will unveil plans to sell or close up to one-quarter of its businesses in a shake-up designed to bolster its finances and reinvigorate its flagging share price.

The company, whose weak stock market performance led to the removal of former Chief Executive Andrew Moss in May, will say it aims to offload or shut about 15 of its 58 business units at an investor presentation in London, a source familiar with the matter said.

The retrenchment plan follows a review of the group launched by new Chairman John McFarlane, the ex-banker who became acting CEO after Mr. Moss left, aimed at identifying and jettisoning underperforming operations.

Businesses and assets earmarked for disposal could include Aviva's operation in the United States, acquired in 2006 for £2 billion ($3.14 billion), as well as its minority stake in Dutch insurer Delta Lloyd Groep, analysts have said.

The company also will set out targeted savings from a previously announced plan to thin out a layer of regional management that costs about £100 million ($157.0 million) a year, the source said.

Cost savings and disposal proceeds would be used to strengthen Aviva's capital reserves, seen as vulnerable because of the insurer's heavy exposure to the ailing eurozone, where it made 40% of its operating profit last year.

Aviva holds eurozone government bonds to generate income on behalf of its customers in the single-currency area, and sharp falls in their value wiped almost one-third off the company's regulatory capital buffer between July and September last year.

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Worries over Aviva's heavy exposure to the ailing euro area have contributed to a 37% slump in its share price over the past year, lagging a 12% fall in the Stoxx 600 European insurance index.

Shares in Prudential P.L.C. and Legal & General Group P.L.C., Aviva's biggest British rivals, have risen 2.5% and 0.6% over the same period.

But analysts reckon Aviva on Thursday could dispel worries it might cut its dividend payouts, among the highest in the British insurance industry relative to share price.

"We may get some sort of steer on the dividend, and the way it's looking to me is that they will maintain it rather than cut it," said Panmure Gordon analyst Barrie Cornes.

Mr. McFarlane said in a conference call with analysts in May that dividend cuts would not yield big enough savings to significantly bolster its capital, Mr. Cornes said.

The slump in Aviva's shares closely follows an earlier sharp decline triggered by the 2008 banking crisis which investors say was exacerbated and prolonged by strategic mis-steps, including an unpopular dividend cut the following year.

The latest overhaul at Aviva builds on a shake-up launched in 2010 by Mr. Moss under which the insurer sold assets including its RAC breakdown service and some eastern European units, reducing the number of countries it operates in to 21 from 30.

The company is also in the process of selling small-scale businesses in Sri Lanka, Malaysia and South Korea.

But analysts say a lack of buyers in the faltering economies of North America and Europe, home to Aviva's biggest units, means there is limited scope for large-scale disposals, or for radical moves such as splitting the group's general and life insurance arms.

"Until the euro situation is resolved one way or another, the shares will suffer," Investec analyst Kevin Ryan said.