Gran Canaria (2019–2024) In the
2019–20 season, Montero began playing for Gran Canaria B, the
reserve team of
Liga ACB club
Gran Canaria, in the third-tier
LEB Plata. He immediately became a key player for his team. In his debut on 15 December 2019, Montero recorded 12 points, four assists, and six steals in an 84–65 win over
Menorca. One week later, he scored a season-high 28 points in a 97–89 victory over
Benicarló. On 18 January 2020, Montero collected 27 points with six three-pointers and six rebounds in a 98–82 win over
Pardinyes. On 27 September 2020, Montero made his debut for Gran Canaria's senior team in the ACB, recording five points and three rebounds in 10 minutes in an 88–71 loss to
Zaragoza. On 5 December, he scored 33 points, a career-high in the LEB Plata, and six rebounds in a 95–86 loss to
Navarra. On 17 March 2021, Montero posted 27 points, six rebounds, and six assists in an 82–54 win against Navarra, and was named MVP of Round 21 in the LEB Plata. In the
2020–21 LEB Plata season, he averaged 18 points, 5.7 rebounds, 4.4 assists, and 2.5 steals per game. After his time with
Overtime Elite concluded, Montero would return with the Gran Canaria properly.
Overtime Elite (2021–2022) On 4 June 2021, Montero was
loaned to Team Overtime of
Overtime Elite (OTE) for the league's inaugural season. In 24 games, he averaged 16.9 points, 6.1 rebounds, 4.7 assists, and 3.4 steals per game, leading OTE in scoring. Montero went undrafted in the
2022 NBA draft. He joined the
New York Knicks for the
2022 NBA Summer League.
Real Betis (2023) In 2023, Montero would sign with
Real Betis Baloncesto in the Spanish
Liga ACB.
Andorra (2023–2024) Following his brief time spent with Real Betis, Montero would sign with
BC Andorra in the Spanish
Liga ACB.
Valencia Basket (2024–present) On July 9, 2024, he signed with
Valencia of the Spanish
Liga ACB. In the
2024–25 EuroCup Basketball season he led Valencia in points (13.2) and assists (5.3) per game, and had a team-best PIR of 15.9, as the
Taronja made it to the semifinals of the competition. ==National team career==