As he was released from his initial contract and signed a new contract to receive the bonus, he would have been eligible in the 2011 Rule 5 draft if not added to the Cubs' 40 man roster. On July 9, 2011, Szczur was assigned to the High-A Daytona Cubs' roster. He finished the year batting .293 in 109 games between Peoria and Daytona. On July 27, 2012, he was promoted to the Double-A Tennessee Smokies. He slashed .267/.360/.390 in 113 games between Tennessee and Daytona in 2012. In 2013, Szczur returned to Tennessee where he hit .281/.350/.367 with 3 home runs and 44 RBI. He began the 2014 season with the Triple-A Iowa Cubs before being promoted to the Major League roster. Chicago Cubs On August 16, 2014, Szczur was called up to the Cubs. He made his debut with the Cubs the next day. Szczur recorded his first Major League hit on August 21 against Madison Bumgarner of the San Francisco Giants. He recorded his first career home run on September 13 against Justin Wilson of the Pittsburgh Pirates Szczur split time during the 2015 season between Triple-A and the Majors, ultimately being called up by the Cubs on seven occasions. He finished the year hitting .222/.278/.333 in 47 major league games. On April 29, 2016, he hit his first career Major League grand slam against Chris Withrow of the Atlanta Braves in the 8th inning, putting the Cubs up 6–1. In 2016, Szczur played in 107 games batting .259 with five home runs and 24 RBI. Szczur made no appearances during the Cubs World Series run nor was he on the World Series roster, but still earned his first career championship. Szczur was designated for assignment by the Cubs after only playing in 15 games on May 6, 2017. San Diego Padres The Cubs traded Szczur to the San Diego Padres for Justin Hancock on May 8, 2017. Szczur played in 104 games for San Diego in 2017, batting .227/.358/.364 with 3 home runs and 15 RBI. In 2018 with San Diego, Szczur hit .187 in 57 games. On July 1, 2018, he was designated for assignment by San Diego and sent outright to the Triple-A El Paso Chihuahuas. He declared free agency on October 2, 2018. Arizona Diamondbacks On December 14, 2018, Szczur signed a minor league contract with the Arizona Diamondbacks organization. Szczur spent the year