Contreras, 24, was promoted to the Cubs on June 17 and made a splash by hitting a home run on the first pitch he saw two days later. He began the season No. 50 on MLB.com's Top 100 list. In the latest rankings, he is No. 23.
According to the Top 100 list, the Cubs' top three prospects are Contreras, Ian Happ and Eloy Jimenez. Happ was No. 76 on the preseason Top 100 list and now is No. 31, while Jimenez, who was not included on the preseason rankings, is now No. 33.
To be eligible for the list, a player must have rookie eligibility. To qualify for rookie status, a player must not have exceeded 130 at-bats or 50 innings pitched in the Major Leagues, or accumulated more than 45 days on the active roster of a Major League club or clubs during the 25-player limit period, excluding time on the disabled list or in military service. Contreras currently has 117 at-bats with the Cubs, and was hitting .282.
Happ, 21, was the Cubs' first-round pick in the 2015 Draft, and is batting .293 in 30 games at Double-A Tennessee. He began the season at Class A Advanced Myrtle Beach, where he hit .296. This season, Happ has combined to hit nine home runs, 25 doubles and three triples, with 13 stolen bases. He was named the Cubs' Minor League Player of the Month for June after batting .422 in a combined 26 games for Tennessee and Myrtle Beach.
Jimenez, 19, was batting .332 with 11 home runs, 30 doubles, one triple and 64 RBIs in 89 games for Class A South Bend. He starred at the SiriusXM All-Star Futures Game, hitting a three-run homer and a double, and he made a great catch in right field.
Rounding out the Cubs' top 10 are third baseman Jeimer Candelario, right-handed pitcher Dylan Cease, outfielder Mark Zagunis and right-handed pitchers Duane Underwood, Oscar De La Cruz, Trevor Clifton and Jose Albertos.
Zagunis, 23, a third-round pick in 2014, and Clifton, 21, a 12th-round selection in 2013, were ranked 18th and 21st in the preseason list, and Albertos was not included in the Cubs' Top 30. Zagunis hit .302 at Tennessee and was promoted to Triple-A Iowa, where he was batting .272 with five home runs, 12 doubles and four triples. Clifton was 5-6 with a 3.32 ERA in 17 starts at Myrtle Beach.
Albertos, 17, is just beginning his professional career with the Cubs' Rookie League team in Mesa, Ariz. In his first start on June 22, he struck out seven over four scoreless innings and gave up one hit.
Reliever Carl Edwards Jr., called up to the Cubs on June 20, was listed at No. 15 on the team's top 30 list.
Right-handed pitcher Thomas Hatch, the Cubs' third-round pick in this year's Draft, entered the team's Top 30 list at No. 16.
The ranking of baseball's top prospects is done byDraft and prospect experts Jonathan Mayo, Jim Callis and Mike Rosenbaum, who compile input from industry sources, including scouts and scouting directors. It is based on analysis of players' skill sets, upsides, proximity to the Majors and potential immediate impact to their teams. Only players with rookie status are eligible for the list. The rankings follow the Collective Bargaining Agreement guidelines for which players fall under the international pool money rules: Players who were at least 23 years old when they signed and played in leagues deemed to be professional (Japan, Korea, Taiwan, Cuba) are not eligible.
Carrie Muskat has covered the Cubs since 1987, and for MLB.com since 2001. She writes a blog, Muskat Ramblings. You can follow her on Twitter @CarrieMuskat and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.