Mateianu was born in Lipănești, Prahova and started playing football in the Romanian lower leagues at Flacăra Boldești and Progresul CPCS București.

[1][5][7]In 1957, during a football tournament held in San Sebastián, Spain in which he participated with one of Romania's youth teams, Mateianu had an offer to play for Real Madrid, which he refused, not wanting to risk to never see his parents again, as he could have not been allowed to return to the country by the communist regime.

[1] Mateianu played six games and scored two goals at international level for Romania, making his debut under coach Augustin Botescu at the 1960 European Nations' Cup quarter-finals where they were defeated by Czechoslovakia, who advanced to the final tournament.

[13][14][15] He played three games and scored two goals at the 1966 World Cup qualifiers, making his last appearance for the national team in a friendly which ended with a 2–0 loss against East Germany.

[3][4][5][6][8][10][12][9][16] During his period spent at Baia Mare, Mateianu became known for his coaching innovations, having many tactical schemes which he gave them names like Morișca ("The Hand-Mill") in which the strikers and midfielders swap places during the game, being considered an early form of tiki-taka, Momeala mare ("The Big bait"), Momeala mică ("The Little bait"), Căciula ("The Hat"), Paralelogramul ("The Parallelogram"), Americana ("The American"), Fundul de sac ("The bottom of the bag") or Șarpele ("The Snake") are only a few examples.