 At the start of the 2015–16 campaign, Agirretxe was in the best goalscoring form of his career, scoring 12 times in the first 13 league matches.He suffered an injury to his left ankle during a loss to Real Madrid at the Santiago Bernabéu Stadium on 30 December 2015, and returned sooner than expected the following February, netting in a 1–1 home draw against Málaga after only seven minutes on the pitch.Shortly after, however, he relapsed from his ailment, going on to be sidelined for more than one year; in June 2016, while absent from playing, he renewed his contract until summer 2020.