BARCELONA/LONDON, Jan 11 (Reuters) - Grifols told investors on Thursday it did not foresee any problems in closing the $1.8 billion sale of its stake in Shanghai RAAS, despite a plunge in its shares following the publication this week of a Gotham City Research report questioning the Spanish drugmaker's accounting.

Grifols shares fell as much as 16% Thursday after the company held a conference call to reassure its investors. The company's shares have lost more than 28% of their value since the Gotham City report surfaced on Tuesday.

Grifols Vice Chairman Raimon Grifols told investors that the sale of 20% of Shanghai RAAS Blood Products should close as planned in the first half of 2024, although there would be no penalty if it is cancelled. Proceeds from the Chinese sale will be used to repay part of Grifols' debt in 2025.

Grifols CEO Thomas Glanzmann said there was room to improve communication and governance at Grifols, but said short-selling fund Gotham City had suggested irregularities using information that had already been signed off by auditors and regulators.

"We categorically deny and reject all these allegations," Glanzmann said, adding that Gotham City was acting "for pure self-interest and financial gain."

Chief Financial Officer Alfredo Arroyo Guerra said on the same call that Grifols was working to simplify its structure and that future transactions "will be straightforward."

Barcelona-based Grifols, which makes drugs from human blood plasma, announced Wednesday that it would take legal action against Gotham City, whose report reduced its market value by $2.5 billion. It declined to say when or where it would do so.

Grifols officials said they would provide information requested by the Spanish stock market supervisor CNMV "as soon as possible" and within 10 days.

In its report, Gotham City questioned Grifols' reported debt and earnings before interest, taxes, depreciation and amortization (EBITDA), as well as its leverage ratio of 6.7 times. Gotham claimed that the actual leverage ratio was between 10 and 13 times EBITDA.

He also questioned the financial links between Grifols and Scranton Enterprises, an investment vehicle linked to Grifols' founding family.

Glanzmann said the family owns less than 20% of Scranton and that interactions between Grifols and Scranton have been "on arm's length terms."

In a post on social networking site X, Gotham City said it has "many questions and observations about Grifols."

It said one of its allegations had not yet been addressed: that both Grifols and Scranton fully consolidate blood donation company Haema AG and plasma donation company BPC Plasma in their accounts. Grifols sold both to Scranton in 2018.

From Grifols, Arroyo Guerra told investors that the company is required to consolidate both entities because it holds a call option, adding, "Rest assured 100% that this company has always followed accounting standards."

The board of the Spanish Association of Minority Shareholders of Listed Companies (AEMEC) said it expects to decide on Friday what legal action, if any, to take, including a possible complaint against Grifols or Gotham City.

AEMEC was still analyzing the facts reported by Gotham City to determine whether Grifols had done anything wrong, its spokesman told Reuters.

(Additional reporting by Jesus Aguado, editing by Andrei Khalip, editing by Alexander Smith; Spanish editing by Tomás Cobos)