Activist investor Starboard Value has taken a stake of about $1 billion in Pfizer and wants the U.S. drug giant to make changes to turn its performance around, sources familiar with the matter said on Sunday.

Pharmaceutical giant Pfizer (PFE) is seeing stock gains in Monday's pre-market trading after activist investor Starboard Value took up a $1 billion stake, according to a Wall Street Journal report. Yahoo Finance senior health reporter Anjalee Khemlani covers Starboard's reported investment in Pfizer as the pharma company seeks to reposition itself coming out of the COVID-19 pandemic.

Starboard has reached out to former Pfizer CEO Ian Read and ex-finance chief Frank D'Amelio, and both have expressed interest in supporting the activist investor's turnaround efforts, reports said.