The midfielder had come through the youth ranks at Athletic, but made just the one appearance in the senior team before making the move to Betis in 2009.
Alonso has struggled with injuries in the second-half of the season and has not been given the all-clear by Real Madrid's doctors to take part in the competition which starts on June 15.
It was a great weekend in the Spanish La Liga in which top teams displayed just why they are the leaders.
Real Madrid suffered a major setback to their Spanish title hopes when they slumped to a 1-0 defeat at Real Betis on Saturday, handing Barcelona the opportunity to open an 11-point gap over their bitter rivals on Sunday.