Sollecito's defence said it will make the complaint to Italy's Superior Council of Magistrates, which disciplines judges, after the chief judge at Sollecito and his former American girlfriend Amanda Knox's retrial for Kercher's murder gave media interviews at the weekend commenting on last Thursday's guilty verdict.
"We are also considering other initiatives," said Sollecito's lawyer Luca Maori.
Trial judge Nencini's interviews were controversial as Italian courts do not generally comment on cases before publishing their written reasoning for a verdict, which are issued up to three months afterwards.
Judges in Italy are banned from commenting publicly until after the final appeal to the Supreme Court, which in Knox’s case will not happen until next year.
Defence lawyers interpreted Nencini's comments as evidence that the panel of judges and jurors was biased, claiming the judges would have acquitted Sollecito if he had incriminated Knox and questioned the legitimacy of the verdict itself.
Among Nencini's comments were remarks stating that if Knox had gone to work on the evening of Kercher's killing, the murder would most probably never have happened.
But he seemed less convinced of Sollecito’s guilt and said the Italian could have helped his case if he had submitted to cross-examination.
Sollecito said he was "dismayed" by the remarks.
In an interview with La Stampa, another Italian newspaper, he asked "If my testimony could have really changed the course of the trial, why did (no one) feel the need to question me?" he asked.
Nencini's remarks angered Nicolo Zanon, a conservative member of the Italian judiciary, CSM. On Monday, he said he and three of his peers would ask the CSM to take action against the judge.
Sollecito and Knox were sentenced to 25 years and 28 years and six months respectively for Kercher's brutal 2 November 2007 slaying. She was found semi-naked in a pool of blood, with her throat slit and 40 wounds to her body in the flat she shared with Knox in the Umbrian city of Perugia.
In the long-running legal saga, Sollecito and Knox were first convicted of Kercher's murder in 2009 and sensationally acquitted by an appeals court in 2011 before Italy's supreme court in 2013 order a re-trial.
A third person, Ivorian-born drifter Rudy Guede, was tried separately and convicted of Kercher's murder. He was jailed for 30 years in 2010 but his sentence was reduced to 16 years after two rounds of appeals and the judges' conclusion that he had not acted alone.