On 13 August 2008, Aarón joined Scottish Premier League club Rangers on a two-year loan deal, with an option to buy. He made his official debut in the 7–1 defeat of Hamilton Academical on 6 December, coming on as a second-half substitute and immediately creating a goal for compatriot Nacho Novo. He scored his first competitive goal for his new team in a Scottish Cup tie against Third Division side Forfar Athletic, and was booked for removing his shirt in celebration; his second also came in the Cup, against Hamilton from the penalty spot, in what was his first start. On 7 June 2009, it was announced that the two-year loan would be terminated, and Ñíguez returned to Valencia late in the month.
Return to Spain
On 30 August 2009, still on loan from Valencia, Aarón joined RC Celta de Vigo in division two, appearing in less than one third of the matches during the season due to a serious anterior cruciate ligament injury. For 2010–11, in the same situation, he moved to another club in that tier, Recreativo de Huelva. In July 2011, Aarón terminated his contract with Valencia and signed a five-year contract with another side in the second division, UD Almería. On 7 January 2013, just hours after being released by the Andalusians, he joined another team in that level, Elche CF, penning a deal until June 2017; he appeared in 16 matches for the latter, which were promoted to La Liga after a 25-year absence. Aarón made his debut in the Spanish top flight on 19 August 2013, starting and being booked in a 0–3 away loss against Rayo Vallecano. On 31 October he scored his first goal in the competition, netting his side's last in a 2–2 away draw against Athletic Bilbao. On 12 August 2015, Aarón severed ties with Elche.
Braga
Aarón moved to a third foreign league in late August 2015, signing for S.C. Braga of the Portuguese Primeira Liga. After appearing in only 14 games across all competitions, he left the club.
Tenerife / Oviedo
On 30 August 2016, Aarón signed a one-year contract with CD Tenerife, returning to Spain and its second division. The following 3 July, he agreed to a two-year deal with fellow league team Real Oviedo. A regular starter with the latter, Aarón lost his starting spot after the arrival of Yoel Bárcenas, and terminated his link on 18 November 2018.
On 19 November 2018, Aarón joined Johor Darul Ta'zim F.C. on a five-year contract. On 21 February2019, however, he was released and replaced by Leandro Velázquez.
Málaga
Aarón returned to the Spanish second tier on 4 March 2020, signing with Málaga CF until 30 June.
Ñíguez came from a football family: his father, José Antonio, played several years with Elche – including the 1984–85 season in La Liga – as a striker. His older brother, Jonathan, was also brought up at Valencia, spending almost his entire senior career in the lower leagues. The youngest, Saúl, was brought up at Atlético Madrid.
