PHOENIX — Bad news continues to haunt the Rockies.

Left-handed starter Brett Anderson, who left Tuesday’s game against the Chicago Cubs in the fourth inning because of back spasms, is still in a great deal of discomfort.

He already is on the 15-day disabled list and the fear now is that the back injury could be season-ending.

Anderson underwent an MRI on Friday and the team is still awaiting results of the test.

“He underwent the MRI to see if there is possible disc involvement,” head trainer Keith Dugger said. “We will wait and see on the results, but he’s still in a lot of discomfort.”

If the MRI shows there is an injured disc in Anderson’s back, he likely would be done for the season. According to Dugger, Anderson has previously never had back issues.

Anderson already missed 83 games because of a broken finger suffered during an at-bat. He underwent Tommy John surgery in 2011 as a member of the Oakland A’s.

At the end of this season, the Rockies must decide if they want to exercise their $12 million club option on Anderson’s contract.

The Rockies did receive some good news Friday. Injured shortstop Troy Tulowitzki went through a series of agility drills and took batting practice and felt no pain. It’s possible be could be sent out on a rehab assignment in a week to 10 days. However, manager Walt Weiss cautioned that it’s too early to put a timetable on Tulo’s return.

Tulo update. All-star shortstop Troy Tulowitzki, rehabbing a left hip flexor injury suffered July 19, went through a series of agility drills and took batting practice Friday. He felt no pain and was happy with his workout.

“I felt good out there today,” Tulo said. “I took some groundballs out there and I think I made some progress.”

Tulowitzki was especially encouraged that he was able to work on his lateral movement without discomfort.

“I felt good. That was obviously the next step,” he said.

The next major hurdle is running the bases, but Dugger has not set a timetable for that yet.

It’s possible Tulowitzki could be sent out on a rehab assignment in a week to 10 days. However, manager Walt Weiss cautioned that it’s too early to predict Tulo’s return.

Patrick Saunders: psaunders@denverpost.com or twitter.com/psaundersdp