The left-sider has signed a two-year deal with the Ligue 2 side.
Lionel Messi, Neymar and Luis Suarez all scored as Barcelona overcame a first-leg deficit to beat Athletic Bilbao to advance in the Copa del Rey.
Atletico Madrid brushed aside Guijuelo to advance to the last 16 of the Copa del Rey, while Malaga were eliminated by second-division Cordoba.
Deportivo La Coruna have reached an agreement to sign Romania forward Florin Andone from Cordoba, subject to a medical.
Leganes were promoted to the top flight of Spanish football for the first time in their history after wining on the final day of the Segunda Division.
Cameroon international Patrick Ekeng died after he collapsed during a match with Dinamo Bucharest in the Romanian capital on Friday, doctors said.
Crespo, 28, began his career at Sevilla before playing for Racing Santander, Padova, Bologna and Verona.
Luis Suarez scored his first hat trick for Barcelona and Lionel Messi bagged a brace as Cordoba lost 8-0 and were relegated from La Liga.