According to Sahadev Sharma of The Athletic, De La Cruz tested positive for the banned diuretic and masking agent Furosemide.
The 23-year-old De La Cruz has struggled this season for the Double-A Tennessee Smokies.
In 16 starts, the 6'4" righty is 6-7 with a 5.24 ERA and 1.38 WHIP. While he has struck out 73 batters in 77.1 innings pitched, he has also allowed 76 base hits.
De La Cruz has dropped off significantly compared to last season, which he split between High-A and the Arizona League.
In 13 outings last season, he was 4-3 with a 3.34 ERA and 1.20 WHIP.
The Dominican Republic native once looked like a future ace, going 8-1 with a 1.80 ERA in the Dominican Summer League in 2014.
Although De La Cruz is on Chicago's 40-man roster, he wasn't likely to play a role for the Cubbies down the stretch this season.
He could have been a trade chip ahead of the deadline, but the suspension almost certainly will prevent that from being the case.
De La Cruz will be eligible to return to game action next season.