OAKLAND -- With every stride after he'd handed the ball to Boston Red Sox manager John Farrell in the third inning Tuesday night, Justin Masterson's pace grew ever slower, as if he was contemplating whether there was someplace other than the dugout he could go. The hourglass had emptied by the time he arrived.

"I was mad at the time, because part of me wanted to stay in and like, 'Just let me go, just let me keep going. It may not be pretty right now, but in one sense let me work through it out here,'" Masterson said after Boston's 9-2 loss to Oakland, which ended the A's six-game losing streak.

"This was one of those days that they weren't missing anything going back to the middle. Let me work through it; slow it down and here we go.

"I was fired up. Human, you know. The human side of me came out. This was not fun. I would have at least liked to continue on. He [Farrell] jumped out there a little quick, but I understand he was just looking out for me. [But] it wasn't fun tonight, I'll say that. It wasn't fun."

Justin Masterson lasted just 2 1/3 innings against the A's after he gave up six runs on six hits that included two home runs. Ed Szczepanski/USA TODAY Sports

From Farrell's perspective, leaving him in was an option that did not exist. Not after Masterson, coming off a start in which he walked six batters in just 4 1/3 innings, was putting his pitches on a tee for the Oakland Athletics, who scored three times in the first, scored another in the second and would tack on three more in the third, two charged to Masterson. The A's had hit for the cycle -- two home runs, triple, double and two singles -- by the time Masterson registered seven outs.

Farrell not only pulled Masterson on Tuesday night, but suggested that there might be issues that require him to take the 30-year-old right-hander out of the rotation, although he wasn't prepared to commit after the game to doing so.

Knuckleballer Steven Wright, who relieved Masterson and finished the game, allowing three runs on six hits, would be the obvious candidate to make Sunday's start in Masterson's place if Farrell determines a change is warranted.

"The last two times out for Justin have not been anywhere close to what he's shown this year -- set aside prior to the start of 2015," Farrell said. "Clearly, he's not right. Whether that's physical, whether that's delivery-wise, the ball is not coming out of his hand as he's shown the better part of the year. We've got to gather information, we've got to check on him in the morning, get a full workup, get a better assessment of where things are."

Masterson had established himself as one of the better starters in the league -- an All-Star with Cleveland in 2013 -- until he suffered a calamitous tear of his oblique muscle near the end of the 2013 season. That injury was a likely suspect in the shoulder impingement that followed, and Masterson also had inflammation in his right knee. The injuries led to a fractured 2014 season, one in which his velocity dropped dramatically, and he was shipped off to St. Louis, where he bombed and was a nonfactor in the Cardinals' playoff run.

How concerned are the Sox that Masterson, who has a 6.37 ERA and two no-decisions and two losses, in that order, in his past four starts, is dealing with a physical issue?

"Talking to the medical staff right now and to Justin himself, it's not anything glaring -- an area of the body that can be identified to say this is the primary reason," Farrell said. "To what extent he feels something that might subconsciously be in there and not allow him the freeness and the ability to cut the ball loose, that's what we're trying to work to the bottom of."

The Red Sox decided that it was an acceptable risk to sign Masterson as a free agent to a one-year, $9.5 million contract last December, believing a return to health would make a difference. But to date, Masterson has not come close to regaining the velocity he once had -- Fangraphs.com measures his average velocity at a career-low 87 miles an hour. And while the Sox felt that his sinker-slider combination would work even if the velocity was down, that doesn't compute when he can't spot his pitches.

"Consistency to the action of pitches," Farrell said when asked how Masterson's past two starts have differed from those that preceded them. "The sink isn't as abrupt as it's entering the hitting zone. The action of those pitches are a little bit longer and, obviously, easier for hitters to adjust to."

Masterson said that from the time he warmed up Tuesday he never felt comfortable, in a place in which he has never won (0-6 with a 7.26 ERA in seven starts).

"Once the game came, every single pitch, I try to take the ball in, I leave it over middle, homer," he said. "Try to take it away, everything just kind of ran back to the middle. That's not what we're trying to do."

Masterson, touching the area of his oblique, admitted that it felt "a little bit different, yeah, and that's probably why."

He had admitted earlier this season he was uncertain how much of his velocity would return. Asked if he was disappointed at where it was now, he said: "Today was really disappointing. I was laboring a little too much to be getting 86s and 87s out there. Last game I was laboring, see 89, OK. I go back to the idea it wasn't comfortable, as far as mechanics, to say, ‘Here we go,' and even at 88 and 89 get behind the ball."

But unless the Sox medical staff determines there's a definite physical issue, Masterson is not prepared to surrender his spot in the rotation.

"As we discuss right now, I think I'm more than capable, simply because coming into today I really don't think it's anything too extreme at this point," he said.

"I think right now, we've taken quite a few steps forward, maybe now we're taking one back, but l still think it's a point maybe you have to go back a second to continue to go forward. That's why I don't really think time off right now would be great."