A youth product of hometown club Botev Vratsa, he spent two seasons with the first team, before switching to in 1975. He played 234 matches for the club in the A Group, scoring 54 goals. Yonchev was a key part of the CSKA"s team that reached European cup quarterfinals in the 1980-1981 season and European cup semifinals in the 1981-1982 season.
On 4 March 1981, he netted CSKA"s only goal in a 5–1 loss against Liverpool at Anfield, in their quarter-final first leg tie.
On 3 April 1983, he scored two goals as CSKA beat Spartak Varna 4–0 in the 1983 Bulgarian Cup Final. After nine seasons at CSKA, Yonchev joined Slavia Sofia in 1984.
Player Coach.