It turns out that the mystery (convenient) knee problems that reliever John Grabow developed earlier this year when he was stinking were real problems. And they’re back. Grabow is expected to go on the disabled list today.

Grabow entered Monday’s game against the Pittsburgh Pirates in the seventh inning and retired the first batter, then gave up an infield single to Ronny Cedeno. Paul Maholm squared to bunt on a 1-1 pitch, and Grabow finished the pitch awkwardly. Athletic trainer Mark O’Neal went to the mound and Grabow immediately headed to the clubhouse.

“It’s pretty bad,” Grabow said. “It’s something I thought I could pitch through and it got worse. I’ll go get it checked out [Tuesday].”

Grabow has received a cortisone shot already this season in the knee and was on the disabled list from May 31 to June 15 because of it. In his previous outing Thursday, he gave up one hit over two innings against the Mariners.

“I tried to pitch through it and today it felt a little different, and it kept getting worse and worse to the point where I couldn’t take it any more,” Grabow said.

The injury is unfortunate given that Grabow had actually started to pitch well since returning from his last stint on the disabled list (I know, bite my tongue).

The Cubs are expected to call James Russell back up to the big club, assuming they want to replace Grabow with another lefty.