Chicago manager Lou Piniella made the announcement after the second game of Wednesday's day-night doubleheader against the Atlanta Braves, which the Cubs swept by scores of 10-2 and 8-0.
Before the first game, Piniella said Samardzija was one of the options. The rookie right-hander has not started since July 20, when he went six innings for Triple-A Iowa.
Rich Harden's Tuesday start was postponed by rain, and he was originally scheduled to go Sunday in the series finale against the Florida Marlins. He started Wednesday's night game and threw 92 pitches over five innings.
"I can't bring Harden back on short rest, but I can bring [Jason] Marquis back possibly," Piniella said about his options for Sunday. "By [Marquis] pitching the day game, it gives him a little longer time. If not, we'll either pitch Samardzija or pitch Marshall."
Marquis was willing to work on short rest.
"I would love to go Sunday," Marquis said. "I've done it numerous times in my career. I feel comfortable doing that. I work hard between starts, so I'll be able to do stuff like that."
Instead, it's Marshall, who did pitch one inning in relief on Wednesday. The left-hander has made three starts for the Cubs this year and is the long man in the bullpen.
Samardzija's longest outing so far is 2 1/3 innings against Pittsburgh on Aug. 3, which also was the most pitches he's thrown (40) in his eight outings so far with the big league team. In his last appearance on Sunday, he threw eight pitches.
"Like I said when I first got here, I just want to come in and throw whenever they want to give me a shot and take it as far as I can take it," said Samardzija, when told before Wednesday's twin bill that he had a shot at a start. "I'll just try to throw a lot of strikes and get some early action. Obviously, with the doubleheader, someone's going to have to fill in. ... I'm ready for anything. My arm feels good and has felt good ever since I've been here."
Because he has thrown almost every other day, Samardzija said his arm is still strong.
"You're still using your arm as much as if you're starting," he said. "As long as there's rest, I think it'll be fine."
If Samardzija had gotten the call, he would be rid of the pink backpack, at least for one day. The reliever with the least amount of service time carries it to the bullpen for each game.
"That would be a big plus," Samardzija said, laughing. "I've grown to hate it more and more every day, but it's all for fun. It does serve a great purpose -- there's a lot of good snacks and Red Bull. But it's an ugly backpack."
As far as hazing goes, it's pretty minimal.
"I'm sure [if I was in the NFL], I'd be tied to a goalpost and I'm sure this [hair] wouldn't be here," he said.
He's gotten plenty of attention from national media as he makes the conversion from All-America record-setting wide receiver at Notre Dame to Major League pitcher.
"When I don't have to answer football questions any more, I'll be a happy dude," he said. "That's what I'm working on now. Every inning I go out there -- every quick inning that I get outs and get back in the dugout will help."
It's been quite a ride for the right-hander, who began this season at Double-A Tennessee.
"I'm just trying to go with it, talking to guys as much as possible, soaking up as much as I can," he said. "I think we'll look back on it when the season's over. We'll worry about this right now and then take a deep breath, and when the season is over say, 'Wow, this was pretty crazy.'"
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.