Shares of Spanish drugmaker Grifols fell another 10% on Friday, bringing its weekly loss to nearly 40%, after short seller Gotham City Research accused the Barcelona-based company of manipulating its financial accounts.

The drop since Monday is the biggest weekly decline on record amid a surge in trading volumes, according to LSEG data.

When Reuters contacted Grifols this week, the company rejected Gotham's accusations, contained in a report published on Tuesday.

Grifols, which makes drugs from human blood plasma, has also said it will sue the short seller and seek damages.

After Friday's fall, the company's shares were trading at 8.87 euros at 1710 GMT, but up from a low of 8.1 euros ($8.87) hit on Tuesday.

Gotham's report has subtracted more than 3 billion euros from Grifols' value.

(Report by Jesús Aguado and Matteo Allievi; edited in Spanish by Juana Casas).