Marcelo Alfonso Díaz Rojas (Spanish pronunciation: born 30 December 1986) is a Chilean professional footballer who plays as a central midfielder for Liga de Primera club Universidad de Chile.

Díaz came through Universidad de Chile youth academy, and was promoted to the first team in 2004, when he was 18. Making over 150 appearances Díaz was an integral part of the team with the club that won five titles including three consecutive national championships and the 2011 Copa Sudamericana; the club's first international title. In 2012, he moved to Swiss side Basel, where he won two consecutive league titles, before moving to Hamburger SV in 2015.

Díaz has earned over 60 caps for Chile since his senior debut in 2011, and represented the nation at the 2014 FIFA World Cup as well as the 2015 Copa América, winning the latter while being named in the Team of the tournament.

Díaz has earned the nickname of "South American Xavi", as both of them have a great ball control capabilities and excellent passing skills. In June 2015, he scored a 91st minute free-kick goal that helped save Hamburger SV from its first ever relegation from the Bundesliga and is considered to be one of the most important goals in the club's 128-year history.

He made his debut in official matches for the Chilean national team in 2011. He has currently played 61 matches for the country's main team, scoring 1 goal.