Eckstein said the pain is in virtually the same area as a strained left oblique injury that sidelined him in August and September and hindered him throughout the postseason. The World Series MVP will be examined Saturday by Cardinals head team physician, Dr. George Paletta.
"I felt it when I was in the game on Wednesday," Eckstein said. "I tried to work through it in [Thursday's] workout. And then I just decided to be smart and say something about it.
"I'm hoping it's just sore."
It's unclear how long Eckstein will be sidelined. His double-play colleague, Adam Kennedy, has been held out of the first three games due to soreness in his right side, and is not expected to play until early next week.
Cardinals manager Tony La Russa said that due to Eckstein's previous oblique injury, he is more concerned about Eckstein's situation than Kennedy's.
"It's a reoccurrence," said La Russa. "We'll be more careful.
Aaron Miles started in Eckstein's place at shortstop on Friday, with Edgar Gonzalez getting the call at second base. With both starting middle infielders on the shelf, the Cardinals are short for the time being. Miles, Gonzalez, Jolbert Cabrera and Brendan Ryan are the only healthy, active natural middle infielders in camp.
Scott Spiezio provides a potential option at second base if needed. La Russa said that Travis Hanson, who has played second in the Minors, will not be used at that position. Hanson is primarily a third baseman.
Izzy ahead of schedule: Pitching coach Dave Duncan said Friday that Jason Isringhausen is a couple of days ahead of schedule in his throwing program. Isringhausen, who underwent hip surgery last September, is expected to face hitters Tuesday -- two days earlier than originally planned.
"Izzy's going to throw one more [bullpen session] -- it's going to be a light side [session] -- and then probably on Tuesday he'll face some hitters," Duncan said.
The target date for Isringhausen to pitch in a game remains March 15, but Duncan said that conceivably could be accelerated a bit as well.
"He's getting antsy," Duncan said. "And he's feeling good."
Return of Rincon: The last time Ricardo Rincon pitched competitively in a game, Hector Luna was the starting St. Louis left fielder and Oliver Perez was the opposing starter not for the Mets -- but for the Pirates. It was April 18, 2006 -- 319 days ago.
So Rincon didn't hesitate to call his appearance in Friday's game a "big deal." Following major elbow and shoulder surgery last year, Rincon missed the remainder of the season.
He looked sharp in his return, pitching a three-up, three-down fifth inning with a strikeout.
"Tomorrow, I don't know, but today I feel very good," he said.
More good injury news: Kennedy is progressing nicely in his recovery from some pain in the ribcage area. He took batting practice on the field Thursday, then participated in fielding drills and swung in the batting cage Friday.
"I didn't swing 100 percent," Kennedy said. "I was a little bit wary about letting it loose at this point. I didn't want to do any further damage to it."
The list goes on: Yet another Cardinal is dealing with some soreness in the ribcage area. Reliever Russ Springer has yet to pitch in a game, though he is progressing well in his recovery. No date has been set for Springer to take the field in a Grapefruit League contest.
"It's kind of a day-to-day thing," said Duncan. "He's feeling really good and he's doing a lot of work. He's doing a lot of [pitchers' fielding practice], a lot of flat-ground throwing. They're talking about getting him on the mound here soon. But I don't think there's any reason to rush."
First impressions: Josh Kinney's Grapefruit League debut didn't go as planned, but at least Kinney was able to put things in perspective. The right-hander was charged with a blown save after allowing three runs in the ninth in the Cardinals' 6-5 loss to the Mets.
Kinney loaded the bases on a single, a hit batter and a walk, then allowed a game-tying two-run single and a game-winning sacrifice fly. Still, it wasn't quite as discouraging as his Major League debut, when the first batter he ever faced hit a home run off of him last July.
"It's really no news for me having a rough start," Kinney said.
"It definitely wasn't how I wanted to start, but it's something to build on."
Duncan was willing to give Kinney something of a pass. He noted that early spring is tough for pitchers like Kinney who rely heavily on breaking pitches.
Quotable: "It doesn't matter how long it's been. When you face a team you were with, it's always different. You always want to do a little better. I was definitely a little more focused because it was them today. The manager I had, the pitching coach I had. So it was definitely different, and it helped probably, I would say." -- Braden Looper on facing the Mets, for whom he pitched in 2004 and 2005
Weather report: Saturday looks to be similar to Friday. The forecast calls for a game-time temperature of 82, moderate humidity, some clouds and very little chance of rain.
Coming up: Kip Wells makes his Cardinals debut Saturday at Roger Dean Stadium. The Cards will be the home team against their RDS co-tenants, with game time set for 1:05 p.m. ET. Anibal Sanchez will start for Florida. Also on the St. Louis pitching list are Troy Cate, Randy Keisler, Josh Hancock, Randy Flores, Mike Sillman and Brian Falkenborg.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.