KANSAS CITY, Mo. (AP) — Pittsburgh shortstop Jordy Mercer is expected to miss six weeks because of a knee injury, leaving the Pirates without their starters on the left side of the infield possibly until September.

The Pirates put Mercer on the 15-day disabled list Monday, a day after he was hurt in a collision with Carlos Gomez in Milwaukee. Mercer sustained a bruise and a sprained left knee.

Third baseman Josh Harrison went on the disabled list July 7 with a torn left thumb ligament and is expected to miss seven weeks.

"Yeah, it's a challenge," manager Clint Hurdle said before Monday night's game at Kansas City. "The beautiful thing about this game is no other team really cares. So we're going to play on, opportunities to bring next man up or put a new man in. That's what we'll continue to do."

The Pirates began the day 4½ games behind St. Louis in the NL Central.

Jung Ho Kang replaced Mercer on Sunday and will likely take over in the interim. He started at shortstop against the Royals after making 23 starts at third base.

Sean Rodriguez started at third for the first time this season.

Mercer was taken back to Pittsburgh on Sunday night and evaluated by team doctors. They recommended rest and rehabilitation, but no surgery.

"I actually think from what has happened we caught a break," Hurdle said.

The Pirates promoted infielder Brent Morel from Triple-A Indianapolis and transferred first baseman Corey Hart to the 60-day DL.

Mercer was batting .192 at the end of May, but hit .304 in June to raise his average to .242 before the injury.

"If you got my mail, he should have been out of the lineup a long time ago," Hurdle said. "Then he got hot and now everyone wants him in. And now we're throwing our hands up in the air and we can't play without him."

"There's never a good time to lose a player for a month for the player's sake. What I think this will do in a lot of different cases will show the value of what Jordy does on a daily basis that goes under the radar that is taken for granted or not made aware of," he said. "He's a big part of that infield glue. We're going to give an opportunity for a different cast of characters to get involved."