The 26-year-old threw from 90 feet on Monday and plans to throw from 120 feet on Wednesday.
Chacin's shoulder began causing problems before spring training started, so the Rockies shut him down before he was able to get any work in at their camp.
The injury will likely cause Colorado to look at internal options like Chad Bettis, Jordan Lyles, and/or Christian Friedrich to fill in. They have also have reported interest in ubiquitous free agent Ervin Santana, although they do not appear to be one of the frontrunners to sign him. Their current rotation figures to feature Jorge de la Rosa, Brett Anderson, Tyler Chatwood, and Franklin Morales.
Chacin sounded optimistic, but does not intend to rush back and risk re-injuring his shoulder.
If I start feeling good, I'll keep moving [back]. The good thing is I'm feeling good. My ball is coming out good. Everything feels fine, I feel strong. I'm very happy everything is working out."
In over 600 career innings, Chacin has pitched to a 3.61 ERA while calling Coors Field -- which is notoriously hitter-friendly -- home. He's been worth 10.5 wins to the Rockies over that span, according to FanGraphs.
Chacin signed a two-year extension worth $6.5 million last January. He will be eligible for arbitration next season before hitting free agency in 2016.