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4/6/2014 5:24 P.M. ET

Cook 'ready to go' after latest rehab outing

OAKLAND -- Ryan Cook was all smiles as he greeted reporters in the Oakland clubhouse before Sunday's matinee against the Seattle Mariners.

Though he had a rough outing Saturday with Class A Advanced Stockton, Cook said he felt good to go while rehabbing from shoulder problems that have had him on the 15-day disabled list since the end of Spring Training.

Cook said he hoped to be activated for Monday's contest at Minnesota, but on Sunday morning manager Bob Melvin said he did not have his mind made up.

"We'll activate him on the road trip at some point in time," Melvin said. "Which day, I'm not sure."

The plan was for Cook to get in two innings of work with Stockton, but he was able to record only two outs while allowing two earned runs on two hits with two walks and two strikeouts. Still, the valuable right-handed setup man said he was happy with the way his arm felt, despite the subpar results.

"I came out of there feeling like I'm ready to go," Cook said. "Arm feels healthy, I feel healthy. Got that one out of the system hopefully and now it's time to go, as far as I know."

Cook said his past two Minor League appearances last week with Stockton had given him confidence that he was ready to return to duty, saying Thursday's outing served as something of a turning point. The 26-year-old has made 71 appearances for the A's in each of the past two seasons, compiling a 2.30 ERA, 1.11 WHIP and 9.4 K/9 ratio in that span. Clearly, he is champing at the bit to get back on the big league mound.

Meanwhile, Cook also got to watch outfielder Craig Gentry play in his first game of a multicontest rehab assignment as he tries to come back from a balky back. Gentry, who is expected to take over a reserve outfielder role in Oakland when healthy, went 2-for-4 with a double while playing all nine innings in left field for Stockton on Saturday.

"He looks good," Cook said.

Melvin said the plan was to have Gentry play one or two more Minor League rehab games before the manager would make a decision on his return.

"We'll have some tough [roster] moves coming up on both ends of it," Melvin said, referring to the outfield and bullpen.

Fuld gets start in place of struggling Reddick

OAKLAND -- Struggling outfielder Josh Reddick was noticeably absent from Sunday's starting lineup. So were his trademarked long locks of hair, thanks to an overzealous haircutter on Saturday.

But Reddick's absence seemed to be mere coincidence, and not a result of his 2-for-22 (.100) start to the season. For the series finale against the Mariners and right-hander Erasmo Ramirez, A's manager Bob Melvin inserted early-season sparkplug Sam Fuld into the starting lineup in right field, batting seventh.

Asked about the lineup change, Melvin suggested it was more about Fuld than it was about Reddick.

"He's swung the bat well in his recent at-bats, and I want to keep him fresh," Melvin said of Fuld. "It's a little bit of a balancing act with the roster we have right now."

Fuld, 32, made the A's out of Spring Training after putting together a strong camp as a non-roster invitee. He followed that up by going 3-for-9 with two triples in limited action to start the year.

So with Craig Gentry's imminent arrival to Oakland off the 15-day disabled list, Sunday served as something of an audition for Fuld, who is trying to convince the A's that a five-man outfield could work.

Reddick is not the only A's regular who struggled in the opening week of the season, as Josh Donaldson (.091) and Yoenis Cespedes (.200) were also trying to put an end to slumps.

"When you get off to a slow start, whether it's [Donaldson] or Reddick, sometimes you try to do little bit too much," Melvin said. "You're a guy that the team relies on offensively and you get a little frustrated, but he'll get it back."

Emphasis on stats, like A's defense, is shifting

OAKLAND -- With the rise of sabermetrics in recent years, defenses are shifting their alignments more than ever.

For a middle infielder like Nick Punto, it seems like he never stands in the same place twice. This marks his 14th big league season, and the respected veteran said he had seen defensive shifts become much more widespread across baseball.

"I would say the last three, four years, I think sabermetrics has something to do with that," Punto said. "It's just playing percentages. There's so much information on us as hitters now -- where we hit, tendencies -- that it's just probability, just taking a chance. It's definitely more than it ever has been. … It's going to hurt sometimes, but it'll help more often than not."

The A's are constantly making changes to their infield alignments. When Seattle first baseman Justin Smoak comes up to bat, for example, the second baseman moves to shallow right field, the shortstop shifts over to the other side of second base and the third baseman lines up where the shortstop usually does.

While the A's shifts for left-handed power hitters like Smoak are very pronounced, each opposing hitter has his own defensive blueprint. Punto said the A's meet on the first day of every series to go over defensive alignments, noting that sometimes the infielders also make subtle shifts based on the count.

Manager Bob Melvin has been commended for his ability to evolve as a manager and absorb new information, and said the A's have benefited from the new insights that sabermetrics can provide.

"I think last year, production-wise, we were the top team in the league as far as getting productions out of shifts," Melvin said. "So that's something we've been doing for a couple years now."

Worth noting

• Melvin said Tommy Milone, who was skipped in the rotation because of multiple rainouts this week, would throw to Minor Leaguers in Arizona on Sunday before making his A's season debut on Friday.

"It's been a while since he's pitched," Melvin said. "I think it'll be good for him to face some hitters, and he'll be that much more ready for his next start on Friday."

• Right-handed starter A.J. Griffin will stay in Oakland to rehab his injured elbow while the A's travel to Minnesota for the season's first road trip. Melvin estimated it would be a week or two before Griffin resumed throwing.

"He's just going to start his strengthening here soon," Melvin said. "Up until this point it's been rest, but now he'll start the strengthening portion of it."

Alex Espinoza is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.