Marcos's father, Marcos Alonso Peña was best known for his time at Atletico Madrid, 119 appearances over two games, and Barcelona, 124 appearances. He also played 22 times for Spain after rising through their youth ranks including a memorable Euro 1984 campaign. Since hanging up his boots Marcos took up management and has coached at several high profile Spanish sides.
Either side of playing for Barcelona, Marcos played for Atletico Madrid, a side he would later go to manage. In total, he spent five seasons with the side as a player, signing first in 1979 from his hometown club Santander. Known as a tricky right midfielder, Marcos was soon spotted and broke the transfer record to join Spanish giants Barcelona. On leaving Barcelona in 1987 he rejoined the Madrid side.
Marcos spent five years at the Catalan giants between 1982-7, signing at the time as the most expensive transfer in Spanish football, 150 million pesetas. He enjoyed great success with Barca playing alongside greats such as Maradona, Carrasco, Lineker and Zubizarreta.
One of his career highlights for Barcelona was his goal in the 1982-3 Copa del Rey final when they faced arch rivals Real Madrid in Zaragoza. Marcos scoring a spectacular header in injury time to give Barcelona the victory.
Marcos finished runner-up in the Champions League final in 1986 in Seville when they lost on penalties to Steaua Bucharest.
Marcos would return to Atletico Madrid to assist to George D’Allesandro before becoming head coach at Rayo Vallecano in 1995. He successfully kept them in the first division and led them to a memorable victory at the Santiago Bernabeu were they overcame Real Madrid for the first time in the history 2-1.
He returned to his home town team Racing Santander leading them to first division survival in 1995/96 and 1996/97 which included a record-breaking 9-match unbeaten run. After Santander he joined Sevilla FC in the 1998/99 season and went on to lead the side to a tremendous promotion in the 1999/2000 season.
In the 2000/01 season he returned to Atletico Madrid, and was cruelly denied promotion by Tenerife on goal difference. He went on to have spells at Real Zaragoza, Valladolid, Malaga CF and Granada 74.