Behind ace Roy Halladay, if Toronto decides against trading the leader of its pitching staff, Gaston views Shaun Marcum and young left-handers Ricky Romero and Marc Rzepczynski as the leading candidates for the top four spots.
A host of arms, including lefty David Purcey, will be among those competing for the final vacancy.
"He's got to come into Spring Training and try to win a job from one of those kids," Gaston said.
The "kids" Gaston referred to include Brett Cecil, Scott Richmond, Brad Mills and a handful of other pitchers who will be vying for a spot on Toronto's Opening Day roster in 2010. Purcey began this year as the No. 3 arm on the Jays' staff, but early-season struggles led to a prolonged stint with Triple-A Las Vegas.
Purcey, 27, rejoined the Jays earlier this month and has impressed through three starts back in the rotation.
"Purcey has made some strides," Blue Jays general manager J.P. Ricciardi said. "They've done a good job with him. They sped up his delivery. They've got him working a little quicker. His arm action is a little lower. You guys have been around the game a long time, a lot of guys get it at 27, 28, 29. Dave's another guy you put in the mix."
During Saturday's 5-4 victory over the Mariners, the left-handed Purcey walked away with a no-decision after allowing three runs on nine hits in 5 1/3 innings. Pounding the strike zone has been Purcey's biggest issue this season and the two walks he issued against Seattle marked his fewest in an outing for Toronto since April 22.
Since returning to the rotation, Purcey has gone 1-0 with a 2.89 ERA over 18 2/3 innings, during which he has compiled 12 strikeouts and 10 walks with a .257 opponents' average. In his five-start stint with the Jays in April, Purcey went 0-2 with a 7.01 ERA, fanning 26 and walking 17 over 25 2/3 innings with a .282 average against.
"He's getting a little better as he goes out there," Gaston said. "He's pitched three times since he's been back here and I've thought, looking at the way he's pitching now, it's much better than when he started the season here."
That is what Purcey -- a first-round pick by the Jays in the 2004 First-Year Player Draft -- needed to show in order to put himself back on the club's radar. Purcey will likely start again on Friday or Saturday, giving him one more chance to convince Toronto that he can be a serious rotation candidate next spring.
"I can't really think about that too much," Purcey said. "I've just got to go out there and try to make my pitches every time out and we'll see where it leads next year. Right now, I'm just going to try to go out there, I've got one more start, and I'm going to go in and just go after them."
Jordan Bastian is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.