In March 2000, Nuñez signed for Premier League side Sunderland. The transfer fee paid to former club Nacional was reported as £1.6 million plus a possible further £1 million in bonuses.[4]
One theory surrounding his signing is that Peter Reid, who was the manager when Núñez was brought to the Stadium of Light, thought that he had signed Núñez's strike partner at PAOK, Adolfo Valencia, and not Núñez himself. Núñez himself claimed in an interview that Sunderland had thought that Valencia and Nunez's international team-mate Eduardo Bennett, both of whom were of a similar build, were the same player, and had watched both of them play for PAOK and Honduras respectively assuming they had seen the same player twice. In the confusion, they had ended up signing Núñez by mistake, with the diminutive forward being the only Honduran player at PAOK.[5] Sunderland later went to court over the transfer as Nunez was owned by Uruguayan third tier team Uruguay Montevideo at the time of his move to Wearside, although he never played for them.[6][7] Nunez stayed in England for two years before returning to Nacional, after playing just once for Sunderland against Wimbledon in the league[8] and Luton Town in the League Cup.[9] He later played for Pachuca and Necaxa.
Back in Honduras
Núñez returned to his native Honduras in 2004 and he signed for Olimpia in summer 2007[10] and in June 2008 he rejoined Marathón[11] before moving abroad again.
Guatemala
In 2009, Núñez crossed the border to play for Guatemalan side Jalapa[12] and then joined USAC for the 2010 Clausura championship, along with Selvin Motta and former national team goalkeeper Paulo César Motta.[13] In June 2010, he rejoined Comunicaciones[14] before joining Universidad SC the following year.
In February 2013, a historic fine was imposed on a Guatemalan football club after fans of Heredia racially abused USAC's black striker Núñez.[15]
Núñez left USAC in 2017 before joining third tier team Deportivo Ayutla in September 2018.[16]
Victoria
In June 2019, Nunez signed a contract with Victoria, where he would play alongside his son, also named Milton.[17]