A manager since 1994, starting at Setúbal, Diamantino managed that club for a handful of games in two top-flight spells, nearly a decade apart. Additionally at that level, he had two stints in charge of
S.C. Campomaiorense. Diamantino was appointed
Segunda Liga side
S.C. Olhanense's manager midway through
2007–08, having started the campaign at
Varzim S.C. in the same league. In May 2008 he joined Benfica as an assistant coach, under new boss
Quique Sánchez Flores; both left the post at the end of
the season, after which he moved to the youth academy. In summer 2010, Diamantino signed for second-tier
C.D. Fátima, being fired in late November. He moved abroad for the first time in his career to manage
CD Costa do Sol in Mozambique, but his spell at the club ended in October 2013 when Minister of Labour
Maria Helena Taipo expelled him from the southern African country for having called its people "thieves" in protest at a refereeing decision; he returned to the
Moçambola in January 2019, when he was hired at
Liga Desportiva de Maputo. ==Honours==