[4] He was propelled to the first team at only 18 by manager Agustín Gaínza, making his official debut against Liverpool for the season's Inter-Cities Fairs Cup (2–1 home win, 3–3 aggregate triumph); along with fellow teenage newcomer José María Igartua, he was selected for the 1969 Copa del Generalísimo final against Elche CF, a 1–0 victory in Madrid.

On 23 November 1969, during a league match against CE Sabadell FC, he suffered a serious leg injury (fibula and tibia) from which he never fully recovered; after four unsuccessful operations, he retired aged just 24.

He led the side to back-to-back national championships in his second[9] and third years[10][11] but, during this timeframe, also began a bitter rivalry with César Luis Menotti and his FC Barcelona – the Argentine criticised his playing style as authoritarian and his teams as defensive and destructive, and the Spaniard in turn dismissed Menotti as an ageing hippy and womaniser; the culmination of this was the 1984 final of the Copa del Rey, which ended in a massive brawl between the two sets of players.

[13] He was subsequently appointed at RCD Español in the same league, leading them to a best-ever third place in 1987 and the final of the UEFA Cup the following year, but being relieved of his duties in March 1989 after questioning his squad's desire – the campaign eventually ended in relegation for the Catalans.

His first game in charge was a 1–0 friendly win over England on 9 September,[17] and he led the country to the following three major international tournaments, the 1994 and 1998 FIFA World Cups and Euro 1996, being eliminated in the group stage of the second competition[18] and having a run of 31 matches without defeat.

[25][26] Clemente became manager of the Serbia national team on 21 July 2006, being brought in on initiative from Serbian Football Association president Zvezdan Terzić.

New players introduced into the squad included Danko Lazović, Marko Pantelić, Vladimir Stojković and Aleksandar Trišović, while previous mainstays such as Predrag Đorđević, Dragoslav Jevrić, Mateja Kežman, Savo Milošević and Albert Nađ were dropped.

[37] On 20 September 2013, Clemente was named manager of Libya, taking over from Abdul-Hafeedh Arbeesh who was fired after a 0–1 defeat to Cameroon for the 2014 World Cup qualifying campaign.