During the 2011–12 season he became one of the more important Real Madrid Baloncesto B players, coached by Alberto Angulo, and also began to train and travel with the Real Madrid first team. Díez finally debuted in the ACB League, in the match against Assignia Manresa played on 18 December 2011.
In June 2012 he was invited to the Adidas Eurocamp in Treviso (Italy), one of Europe's best showcase for young players. He completed a fantastic tournament, scoring 16 points in the final game, and was named the Eurocamp's top small forward.[1]
During the 2012–13 season he played on loan for ACB League's Lagun Aro GBC. In the preseason he was one of the most outstanding players of his new team, averaging 10.2 points and 4 rebounds. In Week 5 of the Spanish League he had his personal best game with 17 points.
In the summer of 2013, he returned to Real Madrid, becoming a more standard part of the 12-men roster that won the Spanish League championship and finished second in the 2012–13 Euroleague. On 27 August, Díez started the preparation for the pre-season along with his teammates.[2] On 5 October they obtained the first title of the season, the Spanish Supercup, by defeating Barcelona in the final by the score of 83–79.
In September 2014, Díez was loaned again to Gipuzkoa Basket.[3] He was named MVP of week 20 of the 2014–15 ACB season, after obtaining 32 points and 36 in PIR against Andorra. He has also been included in the best team of the 2014–15 ACB season in weeks 15, 20 and 31.
On 19 May 2015, Díez was named the Best Young Player of the competition, after averaging in his second year with Gipuzkoa Basket 12.6 points and 7.0 rebounds per game.[4]
On 8 July 2015, Díez signed a two-year contract with Unicaja.[5] In April 2017, Díez won the EuroCup with Unicaja after beating Valencia BC in the Finals.[6]
On 5 July 2019, Díez signed a two-years deal with an option for a third season with Iberostar Tenerife of the Liga ACB.[7] He extended his contract until 2023 on 3 July 2020.[8]
In July 2010 he played at the 2010 FIBA Under-17 World Cup, in Hamburg (Germany). He led Spain in scoring and rebounding, with averages of 12.9 points and 7 rebounds per game.[15]
In the summer of 2011 he won the gold medal at the 2011 FIBA U18 European Championship, being selected to the All-Tournament Team. He averaged 12.2 points and 10.4 rebounds in 26.6 minutes per game over the competition.[16]
In July 2012 he played with the Spain U-20 national team and obtained the bronze medal at the 2012 FIBA U20 European Championship. Despite being only 19 years old, he was selected to the All-Tournament Team, averaging 14.3 points and 5.9 rebounds per game, with a 56% field goal percentage.[17] Díez was the leading scorer and rebounder for Spain, playing both forward positions.[18]
In the summer of 2013 he won the bronze medal again, this time at the 2013 FIBA U20 European Championship. Dani Díez continued to improve his game to become one of the most important players for Spain, which resulted in him being selected to the All-Tournament Team for the 3rd consecutive year.[19] His averages improved significantly compared to previous years, to 18.7 points (top scorer of the tournament) and 8.8 rebounds per game.[20]
^"New York Knicks Acquire Josh Hart". NBA.com. February 9, 2023. New York Knicks announced today that the team has acquired guard/forward Josh Hart and the draft rights to Bojan Dubljevic and Daniel Diez from Portland.