CINCINNATI -- Padres rookie right-hander Brett Kennedy insisted he felt fine physically after allowing four earned runs in 1 2/3 innings on Friday. But, left knee soreness will prevent him from making his next scheduled start.

"When he bunted the other day … it just didn't look right," Padres manager Andy Green said. "His left knee swelled up on him a little bit. We'll get it checked out and make sure he's OK."

Kennedy came into Friday's start with a 2.81 ERA in his previous three outings, including his first career victory against Colorado, but he walked four on Friday and threw only 44 pitches before being removed from the game in the second inning.

"The ball just wasn't coming out of my hand right," the 24-year-old Kennedy said. "It's something I haven't dealt with before. No excuses, my mechanics were just not there. It made it really tough on our bullpen."

According to Green, Kennedy was having a hard time getting over his front side on Friday but not wanting to make an excuse, didn't immediately divulge the knee issue.

"You like that; that's a young guy trying to soldier on," Green said. "But, at the same time, if you can't execute for your team, you need to be forthright in that moment. He clearly was having difficulty commanding the strike zone, and that's not something we've ever seen from him."

Kennedy is one of several Padres rookie starters looking to solidify their spots for next season. Kennedy is 1-2 with a 6.75 ERA in six starts since being recalled from Triple-A El Paso. He tossed six shutout innings against the Rockies for his first career win Aug. 31.

"He's got a window of opportunity," said Green, "and he doesn't want that to pass by."

Following Sunday's series finale in Cincinnati, the Padres have two of the next four days off, with a two-game interleague series at Seattle sandwiched between. Right-hander Bryan Mitchell will start against the Mariners on Tuesday and left-hander Joey Lucchesi on Wednesday as scheduled. After that, there could be some changes to the rotation.

"We'll make some adjustments," Green said. "We'll squeeze that rotation a bit, go from a six-man to a five-man. No drastic changes the next four days, then we'll announce something going forward."