"I'm sure they're probably keeping it a secret until the end," Marcum said with a smile.
The reality, though, is that Marcum is in line to be Toronto's Opening Day starter on April 5 if he remains on a typical five-day program. That said, the schedule can always be altered and -- with a little more than three weeks still left in Spring Training -- there is always the chance that other factors may affect the ordering of the rotation.
On Thursday, Marcum showed why the Blue Jays are seriously considering him as their new No. 1 starter -- a role that was reserved for ace Roy Halladay for much of the past decade. In a 4-1 loss to the Rays at Charlotte Sports Park, Marcum worked fast, pounded the strike zone and used strong pitch movement to fashion three shutout innings.
"If he keeps going like that," Gaston said, "I would say he's got a good chance to be the Opening Day starter."
For each of the past seven seasons, the Opening Day start fell to Halladay. When Halladay was traded to the Phillies in December, Marcum and left-hander Ricky Romero emerged as the favorites to take over that job. Gaston has repeatedly noted that he might prefer to have a more experienced starter in the rotation's first slot, and Marcum provides precisely that.
Following his performance on Thursday, Marcum said all the right things once again, downplaying the significance of taking the ball against the Rangers for the regular-season opener. Considering he is coming back from a right elbow injury that forced him to miss all of last season, Marcum feels blessed to simply be competing for a starting job again.
After some prodding by reporters, Marcum did finally allow himself to admit that starting on Opening Day would be special.
"It'd be fun," Marcum said. "It'd be an honor to go out there, for them to think that highly of you to put you out there Opening Day. But, other than that, it's still a game you've got to go out there and pitch and do whatever you can to win."
Walton, who has been charged with finding enough innings this spring for the many pitchers in Jays camp -- as well as setting up the rotation for the start regular season -- was not ready to say that Marcum was in line to start the first game of the year. Walton would only say that the 28-year-old right-hander was one of the candidates.
"Shaun would be a candidate for that spot," Walton said, "if everything follows suit once he gets up to six innings, seven innings and everything goes well. I think we've got three or four guys that we can line up for that spot, but he's definitely one of them."
Against the Rays, Marcum allowed just one hit -- a single into shallow right field off the bat Fernando Perez -- and ended with two strikeouts and no walks. Marcum finished with 39 pitches, including 31 strikes, and he might have ended with a lower count had it not been for a fielding error by third baseman Jarrett Hoffpauir in the first inning.
Marcum faced Tampa Bay regulars Jason Bartlett, Ben Zobrist, Evan Longoria and Carlos Pena and used all of his pitches with the exception of his cutter. Marcum is working on improving his curveball, and Walton and catcher Jose Molina raved about the pitcher's changeup. Molina also noted that Marcum looked much sharper than he did in his previous start.
"He had his stuff working today, for sure," Molina said. "He had sinkers, curveballs and changeups working really good today. He was working quick, and when you work quick, that doesn't let hitters get in the rhythm they want to be in. From last time to this time, the changeup was a lot better. It seemed to me he was more comfortable on the mound."
Prior to missing all of last season while recovering from Tommy John surgery on his elbow, Marcum had gone 23-15 with a 3.85 ERA over 64 career starts for the Blue Jays. Marcum's changeup was heralded as his best pitch, even drawing comparisons at times to the offspeed offering utilized by Mets ace Johan Santana.
Walton saw that changeup again on Thursday.
"I look at arm speed," Walton said. "I looked at the arm speed on his changeup today, and it was awesome. You couldn't tell the difference between the arm speed for his fastball or for his changeup. ... They couldn't see it. I couldn't pick it up. They couldn't pick it up. He's just passing all the tests with flying colors right now."
For Marcum, that is all that matters right now -- passing tests and staying healthy.
If he earns the Opening Day nod, that will simply be a bonus for Marcum.
"It doesn't matter to me, and I'm sure it doesn't matter to the other guys," Marcum said. "We just want to -- for me, most importantly -- stay healthy. Whether it's Opening Day or the fifth game, whatever, I don't really care. I just want to stay healthy and pitch."
Jordan Bastian is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.