On Tuesday, Marcum exited his start against Baltimore after just 52 pitches, complaining of pain in his right forearm and numbness in his throwing hand. Marcum said on Thursday that his arm is still tender, but the numb sensation had subsided. The pitcher has been shut down for the season and surgery seems to be a possibility.
While the Blue Jays are hoping the injury isn't too serious in nature, Gaston said the type of symptoms Marcum experienced are definitely cause for concern.
"Any time that you go and have that sort of test," said Gaston, referring to the MRI, "there's always the fear of something being wrong. With the way he had to leave the game -- the numbness in his fingers and his elbow -- there's always a fear of that."
The MRI results that the Blue Jays obtained on Thursday have been sent to arm specialist Dr. James Andrews, who also dealt with Marcum's previous right elbow issue in June. Blue Jays general manager J.P. Ricciardi wasn't willing to say whether or not the club felt Marcum might require surgery.
"I dont know," Ricciardi said. "I'll let you know tomorrow. I don't want to speculate on anything."
Potentially losing Marcum, who is 9-7 with a 3.39 ERA in 25 starts for Toronto this year, to begin next season would deal a serious blow to the Jays. The team is already without right-hander Dustin McGowan, who could be sidelined until May after undergoing right shoulder surgery in July.
There's also the uncertain status of right-hander A.J. Burnett, who has the ability to opt out of his contract and become a free agent at the end of this season. Ricciardi said he didn't believe Marcum's situation would influence the Jays' approach to Burnett's future, though the GM added that Toronto is open to renegotiating the pitcher's contract.
"I don't know if it will impact Burnett," Ricciardi said. "It just means one of the other kids has to step up and go in that role. Hopefully, it won't come to that, but I guess you've got to prepare for the worst-case scenario."
"We'd love to have [Burnett] stay," he added later. "But if someone wants to blow him out of the water, that won't be us. We would think about that, adding some years, but we're not going to get in a bidding war.
"There's got to be an interest on his part to stay, too."
With Marcum sidelined, the Jays will turn to right-hander Scott Richmond to make a spot start against the Red Sox on Sunday. Looking further down the road, Toronto will have a handful of young pitchers vying for rotation jobs behind ace Roy Halladay if Burnett, McGowan and Marcum aren't with the Jays to open next year.
Toronto could have Jesse Litsch, David Purcey, Casey Janssen and Richmond, as well as prospects Ricky Romero and Brett Cecil, in the running for starting jobs for 2009. The Jays might also consider throwing relievers Scott Downs and Brian Wolfe into the mix for jobs, but Ricciardi isn't ready to look that far ahead.
"We might have a young staff, but we'll see," Ricciardi said. "We've got to get to the end of the year first."