OAKLAND -- Injured A's starter Brett Anderson has learned firsthand how difficult it can be to come back from Tommy John surgery, but the lefty took the biggest step forward on Tuesday in his rehab since he was shut down with forearm stiffness on May 19.

Anderson threw about 10-15 pitches on flat ground after long-tossing from 120 feet. He will throw a couple more flat-ground sessions this week, and said he should resume throwing from a mound by some time next week. He had been working out Oakland's facility in Arizona before joining the A's on Tuesday.

"It's another step in the right direction," Anderson said. "You never want to get shut down, but [it's good] to get back to throwing, get back to throwing in a pitching motion, kind of feel like a pitcher again. It's good to be around your teammates and kind of be around baseball again, rather than 110 degrees in Arizona. It's good to be around this level of baseball and feel like you're participating again."

The left-hander had been far ahead of his rehab schedule before being shut down in May, which helped mitigate Anderson's frustration with the setback. He said he hopes to make at least a few starts for Oakland this season, something which seems likely given it's almost been a year since his July 14 surgery.

"It's kind of important for him to get back with us at some point," A's manager Bob Melvin said. "It's not something we're going to push, he's pretty important, but I think based on where he is, there's a decent chance he will be back at some point in time this year."

Anderson also has lost about 20 pounds from his playing weight last season, currently coming in at around 220-225 pounds after working out in his time away from the team.

A's expect to lose Colon to disabled list

OAKLAND -- When right-hander Bartolo Colon was forced to leave Sunday's game in the third inning with a right oblique strain, the prognosis didn't seem good, just based on the problematic nature of those injuries. Before Tuesday's game against the Dodgers, A's manager Bob Melvin confirmed that Colon was likely headed to the disabled list soon.

"I'm pretty certain there's a DL at some point in time here," Melvin said. "There's corresponding moves and some other things that play into it as well. Those oblique injuries can be a little bit difficult, but we just want to make sure we process this thing and don't get ahead of ourselves, figure out what the coinciding move will be."

Colon had an MRI on Monday that confirmed the initial diagnosis, though the results still needed to be examined by Oakland's medical staff to determine the severity of the strain. The starter incurred the injury when he stopped to field a sacrifice bunt attempt by San Diego's Alexi Amarista.

While playing for Cleveland in 1999, Colon suffered a left oblique strain and missed 28 days, perhaps pointing to an extended absence with this injury.

Melvin said on Sunday that right-hander Tyson Ross, who has started 10 games this season for the A's and pitched well in a spot start on Saturday, could be called up from Triple-A Sacramento to replace Colon.

Weeks dealing with leg soreness amid slump

OAKLAND -- When second baseman Jemile Weeks struck out to end the game on Sunday with the tying run on base, it only symbolized the 25-year-old's larger struggles recently.

While most of Oakland's lineup has been hotter than ever in recent games -- the team averaged 8.4 runs during its five-game winning steak, which was snapped with Sunday's loss to San Diego -- Weeks has been mired in a slump. He's 10-for-51 over his last 13 games, lowering his season batting average to .222.

A's manager Bob Melvin revealed on Tuesday that Weeks has been dealing with soreness in his legs, which is one of the reasons Melvin decided to switch him and outfielder Coco Crisp in the lineup, moving Weeks to the second spot. But that hasn't done much to help, with the second baseman just 2-for-11 in the three games since the swap.

Still, Melvin said thinks Weeks will be able to snap out of his funk soon.

"There were a lot of expectations put on him coming into the season," Melvin said. "To this point, he's had a little bit of a down season based on what we saw from him last year, but sometimes that makes you a little tougher when you do come out of it, knowing how to get through these difficult times."

A's push Parker back to Friday for extra rest

OAKLAND -- While left-hander Brett Anderson continues to progress through rehab from Tommy John surgery, A's right-hander Jarrod Parker is much further along, having established himself in the Oakland rotation this season. But even though Parker is two seasons removed from his own Tommy John operation, the organization is still being careful to limit the wear on the rookie.

To that end, the A's switched spots in the rotation between Parker and left-hander Travis Blackley. Parker will now start on Friday against San Francisco, giving him a full seven days of rest since his last outing, and Blackley will start Thursday's series finale against the Dodgers.

Oakland manager Bob Melvin said it was important to look at controlling Parker's innings. Other factors played into the decision as well, like separating Parker and left-hander Tommy Milone from Blackley, who was pitching in the bullpen earlier this season and hasn't gone as deep into games as the other two.

"[Parker] just pitched in Arizona and Colorado, two difficult places to pitch, expended a lot of energy," Melvin said. "We are very careful with him. Maybe breaks up some of the innings-eaters as opposed to some of the guys that might not potentially go as far. We took a look at all those things and we flip-flopped those two."

Parker has gone 3-3 with a 2.82 ERA in 10 starts and hasn't thrown more than 112 pitches in a start. Melvin earlier had a difficult decision to make regarding the righty when Parker had a no-hitter going and high pitch count on June 4 againat Texas, but the rookie eventually gave up a hit in the eighth inning.

Worth noting

• Manager Bob Melvin said outfielder Yoenis Cespedes had his best day of workouts on Tuesday since reinjuring his hamstring, and he seems likely to return to the lineup on Wednesday. Melvin has talked about playing Cespedes as the DH to ease him back but wouldn't rule out him going right back to the outfield.

• Left-hander Jordan Norberto (shoulder strain) was to pitch an inning for Triple-A Sacramento on Tuesday on a rehab assignment. He could be activated in the next few days.

• The A's agreed to terms with five Draft picks on Tuesday, including sandwich-round picks Daniel Robertson and Matt Olson. The pair was at the Coliseum before the game against the Dodgers to meet and work out with the team.