Montiel was first included in a first team matchday squad at the age of 17, remaining an unused substitute in Rayo Vallecano's 3–1 loss at neighbours Getafe CF in the last 32 second leg of that season's Copa del Rey, advancing on the away goals rule.[4] Four days later, he featured in a La Liga game for the first time, playing the final ten minutes in place of Zé Castro as the team lost 10–2 at Real Madrid;[5] aged 17 years and 108 days, he became the youngest player ever to appear for the club in an official match, surpassing Isi by 32 days.[6]
On 24 April 2016, Montiel scored his first senior goal, netting the second for the B's in a 3–0 home win against AD Parla.[7] In the 2016 summer, after the main squad's relegation, he was definitely promoted to José Ramón Sandoval's team.
On 30 January 2018, Montiel signed a new three-year contract with Rayo and was immediately loaned to CD Toledo in Segunda División B.[8] On 31 August, he moved to Deportivo Fabril also in a temporary deal.[9]
Montiel managed to feature in one league match for Deportivo de La Coruña's main squad before returning to Rayo in July 2019; he was subsequently assigned to the main squad in Segunda División. He scored his first professional goal on 8 March 2020, netting his team's last goal before the COVID-19 pandemic in a 3–2 home loss against Elche CF.[10]
On 2 September 2020, after staying more than 20 days without training due to rejecting Rayo's renewal offer,[11] Montiel extended his contract with the club until 2024.[12] He featured in 23 league matches during the campaign, scoring once as his side returned to the top tier after a two-year absence.
On 28 July 2021, Montiel was loaned to Real Oviedo in the second division, for one year.[13] On 14 July of the following year, he moved to fellow league team Levante UD, also in a temporary deal.[14]
