Shares in Fiat Chrysler Automobiles rose more than 18 percent to a six-month high on Wednesday after the company announced plans to spin off its luxury car unit Ferrari and issue a mandatory convertible bond.

"They seem to have sorted out their capital worries in one go," Roberto Lottici, a Milan-based fund manager for Ifigest, said. He added that a spin-off of Ferrari as a luxury name would help boost Fiat's valuation.

In a statement Fiat said investors participating in the $2.5 billion mandatory convertible bond issuance would be entitled to participate in the spin-off and receive shares of Ferrari.

"It looks to me like they've packaged the Ferrari deal , as a pill to help sell the convertible after results that were far from overwhelming," the fund manager said.

Ferrari has an equity value of 5.8 billion euros, according to a Milan broker.

Earlier Fiat Chrysler reported a slightly lower-than-expected rise in third-quarter operating profit with debt higher than expected.

Fiat shares were up 14 percent at 8.70 euros in Milan, after rising to as much as 9.025 euros, their highest level since April 23. (Get the latest quote here.)

The market has long said FCA, with net debt of 11.4 billion euros at the end of September, needed to raise capital to strengthen its balance sheet, as it battles with losses in Europe and a weakening outlook for Latin America.