When the player first arrived at Stamford Bridge, it sparked a huge row with Alaves, whose president insisted De Lucas had already signed for them. He even threatened to report the matter to FIFA's disciplinary panel.
For their part, Chelsea are also thought to believe he joined Alaves, but on an unusual pre-contract which allowed him to play abroad for one season before returning to the club - hence his move to England.
Since De Lucas subsequently failed to sparkle in 20 games for manager Claudio Ranieri, Chelsea were happy to see him head back to Spain last July under the terms of the pre-contract.
De Lucas disputes this, arguing the agreement with Alaves did not comply with FIFA regulations. In the writ, his lawyer argues it is "clearly not a contract" under FIFA rules because of the bizarre clause which allowed for the player to spend his first season outside Spain.
He also claims it was superseded by the four-year contract supposedly agreed with former Chelsea chief executive Trevor Birch - which theoretically tied him to the club until July 2006.
The financial security offered by this lucrative contract and the glamour of Chelsea's Champions League campaign are a far cry from De Lucas's current surroundings.
Alaves were relegated from the Primera Liga last season so De Lucas has been plying his trade in the Spanish second division. His side are now fourth in the table, with promotion by no means certain.
When De Lucas departed for Alaves last summer, a Chelsea spokesman said: "The club thank Enrique for his efforts and wish him well for the future."
Chelsea today declined to comment on the impending court action over the matter.