Toronto will have to look at ways to replace the 185 innings of quality work that Marcum provided in 2010. The 28-year-old led the way for a young Blue Jays rotation with a 13-8 record and 3.64 ERA with 185 strikeouts.
Blue Jays manager John Farrell knows it will not be an easy task to replace that kind of production.
"Having seen him across the field, it's a guy that brought a certain amount of dependability with him to the mound and a competitive nature that [set] an example," said Farrell, a former pitching coach with the Red Sox.
Ricky Romero, Brandon Morrow and Brett Cecil are locked in as the club's top starters. Farrell indicated Monday that top prospect Kyle Drabek appears to be the favorite to take over as the No. 4 starter.
The 22-year-old got his first taste of the Major Leagues in September and went 0-3 with a 4.76 ERA in three starts. The late-season callup was a reward after an impressive season at Double-A New Hampshire. The Texas native went 14-9 with a 2.94 ERA and 132 strikeouts over 27 starts.
"Ricky, Morrow, Cecil, Drabek, then there will be a fifth spot that we will take a long look at internal candidates," said Farrell, listing off his pitchers.
"While Kyle is a premium prospect and a guy we are extremely excited about, we are going to make sure that he's ready and he has been provided the ample time to be Major League-ready."
If Drabek is able to secure a spot in the rotation, that leaves one job up for grabs. The early favorites appear to be right-hander Jesse Litsch and left-hander Marc Rzepczynski.
The 25-year-old Litsch had his 2010 season cut short after nine starts because of right hip labral tear. It was a rough ending to a disappointing campaign in which he finished with a 1-5 record and a 5.79 ERA.
"Jesse is a guy that competes," Farrel said while drawing a comparison to Marcum. "He's not going to overwhelm you with stuff ... but his cutter is a very respectable pitch, and he's somebody that we know is going to be able to control the game and be able to bridge the gap with guys in the bullpen behind him."
Rzepczynski already has started to make his case for next year. Following the 2010 season, the 25-year-old headed to the Arizona Fall League and posted impressive numbers, going 4-0 with a 1.16 ERA. If he is able to continue that success next season, he would be a tough candidate to beat out for the No. 5 spot.
The dark-horse candidate in the race is up-and-coming prospect Zach Stewart. Blue Jays general manager Alex Anthopoulos indicated the 24-year-old is a lot closer to being Major League-ready than most people realize.
Stewart was a candidate for a late-season callup to the Major Leagues, but since his season-innings limit was almost capped out, the club opted to go with Drabek instead.
Stweart, who was acquired in a trade for third baseman Scott Rolen, went 8-3 with a 3.63 ERA last season with Double-A New Hampshire. Even if he doesn't win the job out of Spring Training, he will likely make an appearance in the Majors at some point during the year.
Anthopoulos hasn't ruled out adding another starter to the mix this offseason, but said he was comfortable with the current group he has assembled if he is unable to make another move.
Farrell expects the competition to heat up during Spring Training. Until then, he is keeping an open mind.
"We want to be sure that we are not sitting here today and anointing who we have on our staff," Farrell said. "A lot could change between now and Spring Training, or even Opening Day for that matter."