It was earlier reported that Robert Lewandowski’s agent and Barcelona FC had verbally agreed a three-year deal.
The win over Real Madrid helped Barcelona extend lead at top to 22 points against second-placed Real Sociedad with six rounds to go.
Espanyol, which is winless in its last five league games, hasn't beaten Barcelona in La Liga since February 2009.
Barcelona had signed Ousmane Dembele from Borussia Dortmund in 2017 in a record-deal worth up to 147 million euros (then USD 175 million), including add-ons.
