ST. LOUIS -- Cubs setup pitcher Carlos Marmol, sidelined with a sprained left knee, will throw a bullpen on Monday and could be available as early as Tuesday.

Marmol, who had an MRI on Saturday, threw off flat ground on Sunday.

"This kid's a trooper, he's a gamer," Cubs manager Lou Piniella said Sunday of the right-hander.

Meanwhile, third baseman Aramis Ramirez, who injured his left calf on Friday, also could return during the Cubs' upcoming series at Arizona, which begins Monday. Ramirez has not taken batting practice the last two days.

Piniella also talked to outfielder Milton Bradley, who has been bothered by a groin injury. Bradley, who has made one start since April 12, still wasn't ready to go.

"I will talk to him on a daily basis and we'll see if he's ready to play," Piniella said. "When he's ready, we'll get him in there."

The Cubs are playing shorthanded, and have no backup infielders. On Saturday, Ryan Theriot twisted his left knee but stayed in the game. What if Theriot had to come out?

"I could've put [Aaron] Miles at short, and then my options would've been second base with [Alfonso] Soriano or [Koyie] Hill at third base," Piniella said. "Move [Mike] Fontenot to second or Soriano to second. I don't think we'll have to be this way long. The fact that I had a short bench [Saturday] wasn't the fact that we lost the baseball game."

Hill saw Theriot wince, and grabbed his infielder's glove. He was ready. The Cubs' backup catcher has been taking grounders at third base just in case.

"I'm ready," Hill said. "I'm ready and more than willing."

Carlos Zambrano also was taking grounders on Saturday at shortstop and third. Hill would be a more likely option than the Cubs' Opening Day pitcher.

"It'd be fun," Hill said. "I played there all through college and played short growing up. It's not as unfamiliar as it would appear."

He played second in Spring Training in 2007 for an inning or two because the team ran out of players. He also played second for Team USA in 1999. It's not that far-fetched. Second base would be a little trickier for Hill after his hand injury because of the double play exchanges that need to be made.

Piniella is just hoping it doesn't come to that.

"It is unusual," Piniella said about not having a backup infielder available. "When you're only carrying one extra infielder to start with, you're gambling that it doesn't happen."

He knows nobody is feeling sorry for the Cubs.

"We're not making any excuses about anything," Piniella said. "The team we're playing right now has been playing better than we have. That's all. Injuries are part of the game. You don't necessarily want to see them but that's why you have 25 players.

"It makes it a little more difficult, but you have to tough it out and win some baseball games," he said.