"I got the call and was like, 'Oh, man, I've got to completely change how I pack,' " Moss said. "You never know. They say always be prepared, but you never know."
Casey, who left Friday night's game with a right hip strain, was placed on the 15-day disabled list on Saturday, leaving the Sox with a hole in their already thin roster.
"As all good players do, they try to talk themselves into being OK," manager Terry Francona said. "He's probably not OK, and we're not in a situation right now where we can wait three or four days to check, because last night, we ended up with no players."
Although the skipper said that Casey made a strong case for his health, the club's medical staff was not convinced that the first baseman could safely go out onto the field. The veteran is expected to be examined again when the team returns home for Monday's off-day.
Moss, who arrived prior to Saturday night's game, has experienced a fair amount of highs and lows already this season. The 24-year-old got the Opening Day start in right field when J.D. Drew's lower back stiffened before the game, only to board a plane back to Pawtucket after the following night's game.
"He's got a really intriguing bat," Francona said. "We actually thought about playing him [on Saturday]. ... He's an interesting guy. If he can play a Major League-caliber first base, that really makes him interesting."
Moss began making the switch from outfield to first base less than a month ago and is slowly becoming more comfortable in the infield dirt.
"The hardest thing is the situational stuff, realizing where to be in certain situations," Moss said. "But the ground balls, that's just a lot of repetition -- it's all a matter of repetition -- but definitely, the situational stuff is a harder thing."
For Moss, who was batting .268 with one home run and 12 RBIs in 22 games for the PawSox, Tropicana Field will be the third dome this year. He went with the team to Tokyo, as the Sox were granted an expanded 28-man travel roster.
When told that he has yet to play a Major League game outside, he laughed and said, "I never thought about it that way."
But like the outfielder-turned-infielder said, in baseball, you never know.
Brittany Ghiroli is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.