Dugger said the Rockies can't determine when the assignment will be "until he takes live BP, and hopefully he can do it before we get home."
Arenado, two games into his rehab assignment at Triple-A Colorado Springs, went 2-for-4 with a double on Saturday and 0-for-4 on Sunday, but made a play in the field reminiscent of his work while winning a Rawlings Gold Glove Award last season as a rookie.
"I'm not really concerned about how he performs; he just needs to get on the field and get his legs back underneath him and get used to game speed again, since he's been out such a long time," Rockies manager Walt Weiss said. "I heard he made a great play, a typical Arenado play where he dives to his backhand side and turns a double into an out. We've seen it many times."
Another sign that his return is imminent is the fact the Rockies are reminding fans on Twitter that he's an All-Star candidate. They're posting Arenado highlights, including Sunday's, with the hashtag #GIFtedArenado.
Fans can cast their votes for starters at MLB.com -- online or on a mobile device -- using the 2014 All-Star Game MLB.com Ballot Sponsored by Experian until Thursday, July 3, at 11:59 p.m. ET. The 2014 All-Star Game will be played at Target Field on Tuesday, July 15 on FOX.
The Rockies also are looking for lefty reliever Boone Logan, who has made two rehab appearances in his comeback from left elbow inflammation, to thrown on back-to-back days before returning, so he could return at the start of the homestand.
Lefty Brett Anderson, completing a comeback from a broken left index finger, is scheduled for 60-65 pitches Wednesday for Colorado Springs in his first rehab contest. He will be in the 75-pitch range in his second start, and could either throw for a third time or return to the Majors at 85 pitches.
Right-handed pitcher Eddie Butler (right rotator cuff inflammation) has thrown two bullpen sessions since the team began its current road trip. Monday was his latest. Butler will face hitters in a live batting practice session after the team returns, then he'll be a candidate for a rehab assignment.
Right-handers Christian Bergman and Jordan Lyles, each out with broken left hands, threw bullpen sessions Monday. Dugger said Bergman was able to wear a glove -- just for balance, because the bone hasn't healed enough to allow him to catch -- and Lyles was not. Return dates for both are uncertain.
Righty Tyler Chatwood, who has a right flexor tendon strain and suffered a setback during a live batting practice session last week, is playing catch.
Outfielder-first baseman Michael Cuddyer, out with a fracture in his left shoulder socket, is exercising, but isn't allowed to perform any motions that jar the shoulder. That means no running or work on an elliptical machine. Cuddyer isn't expected to return until late August.