Berenberg analyst Stuart Gordon downgraded Carnival (CCL) to Sell from Hold with a price target of $10, down from $14.50. The stock closed Wednesday down $1.33 to $19.09.

Carnival's valuation is "highly unattractive" and its capital structure looks "unsustainable" and in need of an injection of new equity, Gordon tells investors in a research note.

The risk of further suspensions of cruises remains high, Carnival's net debt will likely rise significantly and a breakeven analysis suggests the company needs a high proportion of its fleet sailing to generate positive EBITDA, adds the analyst. Gordon does not see enough cash flow to make shareholder returns until at least 2025.