JUPITER, Fla. -- Cardinals right-hander Chris Carpenter has been scratched from his scheduled Friday exhibition start due to a mild left calf injury. However, he fully expects to make his regular-season debut as planned on Thursday, April 9, at home against the Pirates.

Carpenter will throw off a mound on Friday and again three days later.

The righty was running on Monday, a day after his last Grapefruit League game, when he felt discomfort in his calf. He said it was sore on Monday and Tuesday but started getting better on Wednesday. He downplayed the condition and appeared to be walking in the clubhouse with no limp.

"It was pretty good today," Carpenter said Wednesday after the Cardinals' 5-2 loss to the Mets. "They were more cautious, I would say. There's no need to go out and do something Friday. I was running on Monday and my calf pretty much just spasmed up or whatever. It's been sore the rest of the day Monday and pretty sore yesterday, and then this morning I came in and I would say that it's pretty much normal. I'm not sprinting around or anything, but it feels pretty good."

Carpenter expects to throw a bullpen session on Friday and another one on Monday before making his scheduled April 9 start. He has been limited to five games, four starts, over the past two seasons due to elbow and shoulder injuries. In this case, however, all parties are emphatic that the injury is very minor.

"We're just going to err on the side of not pushing it," said manager Tony La Russa. "He was much better today and felt like he could pitch on Friday, but we decided [to be cautious]."

P.J. Walters will start in Carpenter's stead in the Friday night game in Memphis between the Cardinals and their Triple-A affiliate.