Manjezi played rugby for his secondary school, St. Andrew's College in Grahamstown, playing for the first team between 2011 and 2013, captaining the side in 2013. He earned his first provincial selection in 2011, when he represented the Eastern Province at the Under-16 Grant Khomo Week held in Queenstown. He started all three of their matches and scored a try in their game against. After the tournament, he was included in a South African Under-16 High Performance squad. In 2012, despite still being in the Under-17 age group, he was selected to represent Eastern Province Country Districts at the premier schools tournament in South Africa, the Under-18 Craven Week, held in Port Elizabeth, starting a 28–27 victory over Griquas Country Districts. He returned to the 2013 edition of the tournament held in Polokwane. He started three matches and scored tries against the and.
2014–: Under-19, Under-21 and Currie Cup rugby
In 2014, he joined the Eastern Province academy; he was included in the squad that participated in Group A of the 2014 Under-19 Provincial Championshipfor the first time following promotion from Group B at the end of 2013. He immediately established himself as a key player for the team and started all twelve of their matches in the number five jersey. He helped them to sixth position on the log, winning four of their twelve matches. He didn't play any rugby in 2015, but, following serious financial problems at the at the end of the 2015 season which saw a number of first team regulars leave the union, Manjezi was among a number of youngsters that were promoted to the squad that competed in the 2016 Currie Cup qualification series, also being named vice-captain of the team. He was named in the starting lineup for their first match of the season against the, playing the entire 80 minutes of a 14–37 defeat. In July, Manjezi was drafted into the Super Rugby squad and named on the bench for their Round Sixteen match against the.
Cricket
In addition to playing rugby, Manjezi also played cricket at youth provincial level, representing the Eastern Province Under-19 team in 2012 and 2013.
