After working for months with two public defenders, Joaquín Guzmán Loera, the Mexican drug lord known as El Chapo, was in the final stages of hiring a crew of private lawyers in August. Each of them was an expert in criminal defense: One had represented a New York mobster; another had worked for one of Mr. Guzmán’s major rivals; the third had handled the case of a notorious trafficker in Baltimore.

Though at the time it had seemed that Mr. Guzmán would get his chosen lawyers, three months later his all-star legal team had not fully come together. Only one of them, A. Eduardo Balarezo, has overcome the severe restrictions placed on Mr. Guzmán by the government and signed an agreement to defend him. With the trial fast approaching — it is scheduled for April — that has left Mr. Balarezo more or less alone in opposing a dozen federal prosecutors who are ready to assail his client with an arsenal of 90,000 documents, several thousand secret recordings and an army of cooperating witnesses.

“I have no doubt that we can handle the case with the team we have,” Mr. Balarezo said last week, “but I have never worked under these conditions before.”

Chief among those conditions is Mr. Guzmán’s place in isolation in the high-security wing of Manhattan’s federal jail, where he has been locked in his cell since January, sometimes for up to 23 hours a day with no communication with the outside world. Mr. Balarezo first began talking with him about serving as his lawyer in the winter, but it took until September to formalize the deal, he said, because Mr. Guzmán, 57, was unable to confer with his family or associates to arrange payment.