The Spanish side claimed the Tunisia striker reneged on a deal to join them and insist they have documentation to back up their claim, which they say has left them considering legal action. Lassad was introduced to the media at Celtic Park on Thursday lunchtime after signing his two-year deal at the weekend.
Speaking through an interpreter the 26-year-old, who left Deportivo last season, insisted he was not worried about any possible legal challenge to the move, claiming the confusion was down to an agent which whom he had worked in the past, but no longer. He said: "At no point did I have any agreement with Levante to become one of their players."
He added: "What happened was that Levante got in touch with a French agent of mine just before the deadline but I was already in touch with Celtic and decided to sign for them.
"At no point did I have any close contact with Levante so I am not worried by this at all.
"Whatever happened, happened between the agent and the club, not with me directly.
"I have never ever signed any piece of paper from Levante.
"I have all due respect for this club, I played in Spain for long enough and I am well respected in Spain so I have no problem with what happened."
Asked about whether the French agent was still working for him, Lassad said: "No, he is no longer my agent.
"I have worked with him in the past but this agent had nothing to do with the dealings with Celtic."