A historic captain from La Spezia, he is the third player with the most appearances in the history of La Spezia. He arrived in Spezia at the age of 18 and made his debut in Serie C, where the Aquilotti had just been relegated. He played his first match on 7 October 1951 in Rapallo, with the Levantini winning 2-1. Seven days later, he made his debut at the Picco. He scored a goal in that tournament: against Empoli, at the Picco stadium, on 3 December. He played nine consecutive seasons in the white shirt, of which he had become a symbol. He sank into the Promozione league, regained Serie C and the prestigious Coppa Mattei. In 1959, this strapping defender returned to scoring: his goal was decisive in beating Legnano. The match ended 2-1. In the summer of 1960, he was surprisingly sold to Reggiana in Serie B: an offer he could not refuse after a career in the lower leagues. Alfredo Liberi recalls that moment on “peveblog”: 'Although tormented by a thousand doubts and regrets (he felt he was betraying the shirt), one morning in August he plucked up the courage and went to the club's headquarters. He knocked on Del Santo's door and, blushing like a child caught stealing jam, told him about the offer he had received and asked for permission... to leave.
How could anyone say no to a player who had given his all to Spezia for ten years, denying him even his last professional satisfaction? Del Santo agreed, and Zennaro (to the astonishment of the fans) began the championship in Reggio Emilia. But he didn't settle in and returned in November. “There was a transition between the system of play, in which there was no sweeper, and the sweeper,” he recalls today. 'Coach Del Grosso insisted on playing with the system, and I was poorly protected...
They kept getting past us, and we were in trouble. And it was the stopper and the goalkeeper who paid the price. Spezia was also doing badly at that time. President Bertorello, who was fond of me, asked me to return to Spezia: I was in love with this city and the shirt, so I came back." On 4 December, he found his number 5 shirt waiting for him in the dressing room: Spezia-Legnano was like a new debut. Five more seasons followed, which were also prolific in terms of goals: in the 1961-62 tournament, the captain scored against Grosseto, then against Empoli (two goals) and against Rimini, again decisive, in the last minute of the final match of the championship. But it was not enough to save the Aquilotti, who were relegated to Serie D by one point.
He scored three more goals in his decade-long career in the white jersey: against Massese (ending 1-0), against Sestri Levante and against Viareggio in the following match, in which the Aquilotti lost promotion in the ‘fatal’ match against Massa, defeated 4-0 by the Bianconeri. The disappointing 1964-65 season, which left Spezia in Serie D, was also Zennaro's last. On 23 May 1965, against Alassio, he wore his last white shirt, almost fourteen years after his debut.