Both boys came through the ranks at Sociedad, with Xabi making his senior breakthrough in a Copa del Rey match versus Logrones in December 1999. The Londoners paid around £23 million for the Fiorentina left-back, who … Marcos Alonso, younger brother of Xabi, has signed a 5-year deal with Chelsea. Xabi and Mikel Alonso (LaLiga) La Liga Mikel and Xabi Alonso were born to play football and they were born to play for Real Sociedad , the same club their father Periko Alonso played for and coached. Alonso is the son of former Barcelona star Miguel Angel 'Periko' and brother of Tenerife midfielder Mikel.