Williams has been inconsistent this season and sat out the final two games before the All-Star break after getting treatment for inflammation of both ankles.
The Espanyol tie will see Argentine star Lionel Messi take to the field for the first time this year, after a record-breaking 2012 which saw him score 91 goals.
Meanwhile, Britain's other great cycling star, Mark Cavendish , claimed his fourth win of this year's Giro after Friday's 254km leg from Busseto to Cherasco.