Before USL: Greczek was a member of the New York Red Bulls Academy and spent two weeks raining with New York City FC in 2015.
College: Greczek was a walk on at Rutgers University and ended his four-year tenure as the all-time program leader in saves with 372 across 75 games. He posted a 1.72 goals against average and 16 shutouts with the Scarlet Knights. Greczek earned Second Team All-American Athletic Conference and American Athletic Conference All-Rookie Team honors in his first season before leading the Big Ten in saves per game with 4.71 as a sophomore. He recorded eight shutouts as a junior – the most by a Rutgers goalkeeper since 1998 – and was an All-Big Ten Second Team selection, before leading the Big Ten in saves with 101 in his senior year. Greczek played for USL Premier Development League side Jersey Express in the summer of 2016, appearing in seven games and posting 28 saves with one shutout.