BOSTON -- Red Sox manager Terry Francona announced his starting pitchers on Sunday for Tuesday and Wednesday against the Royals.

Right-hander Justin Masterson will make his second start for the Red Sox on Tuesday, coming up from Double-A Portland. Bartolo Colon, the 2005 American League Cy Young Award winner who signed a Minor League contract with Boston in February, will make his Sox debut on Wednesday, coming up from Triple-A Pawtucket.

"It's not etched in stone, but I think we certainly have a plan," Francona said. "But barring weather, which looks nice, or injuries, Masterson will start on Tuesday, then he will go back [to Portland], and Colon will start on Wednesday. Both pitchers have been spoken to. They understand that this is in all likelihood what's going to happen, but if weather gets in the way or something happens, that can change."

Francona didn't reveal which member of the current roster would be demoted to make room for Masterson, but one candidate could be reliever Chris Smith, who was promoted on Sunday from Pawtucket to provide the Red Sox with an extra arm following Saturday's doubleheader.

Masterson, 23, made his first career start on April 24 against the Angels at Fenway Park, going six innings, giving up a run on two hits and four walks, striking out four and becoming the first Sox starter to allow two hits or fewer and pitch at least six innings in a big league debut since Billy Rohr's complete-game one-hitter at Yankee Stadium on April 14, 1967.

Since returning to the Sea Dogs, Masterson, the Sox's fifth pick in the 2006 First-Year Player Draft, has struggled, going 19 1/3 innings, giving up 16 earned runs on 23 hits and 11 walks with 14 strikeouts.

"He's had a few games where, later in the game, he's gotten the ball up over the plate and given up some runs," Francona said. "Early, he's been very good, very consistent, kind of what we've been accustomed to seeing. There's been a few games where late in the games he's runs into a few problems."

Colon, who will turn 35 on May 24, is 2-0 with a 0.64 ERA in three starts for the PawSox. He has made two starts for Pawtucket since recovering from a left oblique strain. In his last start on Thursday in Buffalo, he went six scoreless innings, giving up one hit and striking out four.

Masterson is expected to face Royals right-hander Gil Meche, who is 3-5 with a 5.98 ERA. Colon is expected to be opposed by righty Brett Tomko (2-4, 5.32).

The moves were necessitated by Clay Buchholz, who would have started on Tuesday, being placed on the disabled list on Wednesday with a split nail on his right middle finger. Daisuke Matsuzaka, whose normal day to start would be on Wednesday, would have been pitching on short rest after starting the first game of Saturday's rain-induced day-night doubleheader. Matsuzaka will now pitch on Thursday against Kansas City's Brian Bannister (4-5, 4.29).