Rijo was placed on the 7-day IL at Low-A Cedar Rapids, retroactive to May 25, with a left hamstring strain.
Rijo, who came over to the Twins in last year's Lance Lynn trade to the Yankees, has a 3.47 ERA and a 7.4 K/9 in 36.1 innings. He'll need to improve his strikeout rate and reduce his walks (3.5 BB/9) to thrive at higher levels.