After giving up 31 runs on 41 hits over his last five starts, the right-hander is fighting just to make it onto the Tigers' postseason roster.
Sunday's game against the Orioles at Comerica Park will be his last opportunity to make a good impression before Detroit begins its playoff run.
In his most recent start, against the Royals, Penny was roughed up for seven runs on 10 hits in just four innings for the loss. In the five starts prior to that, he tossed only 25 innings and bumped his ERA up by a half of a run.
Much of his undoing has come from his inability to locate pitches.
"When he hit his spots, he was pitching well," catcher Alex Avila said after the start against Kansas City. "When he didn't, that's when they got the hits. They didn't miss any mistakes."
The similarly struggling Brian Matusz will be on the hill for the Orioles.
Unable to get out of the second inning in his last two contests, the left-hander has surrendered 11 runs on 11 hits over just three innings.
"He's attacking a lot of things that have been a challenge for him, and hopefully he can get a return for it," Orioles manager Buck Showalter said.
"It'd be a nice way to end the season for him. But thinking about what could be, we all know he's capable of better. I just would like to see him get a return for all the hard work he's putting in."
Orioles: Gunning down runners
Baltimore is third in the American League in outfield assists, with 34. Adam Jones and Nick Markakis lead the team with 14 each and are tied for fourth in the AL.
Nolan Reimold has five assists, and Felix Pie has one.
The O's have doubled four runners off first base, and thrown out 13 at second base, three at third base and 13 at home.
Vladimir Guerrero is hitting .392 with seven doubles and two home runs in his last 18 games, with 10 of those being multi-hit games. With his single on Saturday, he tied Julio Franco for the most hits all-time by a Dominican-born player (2,586).
Tigers: Guillen timetable unclear
Though Carlos Guillen's diagnosis of a mild right calf strain didn't surprise the Tigers, the timetable for his return is still unclear.
Guillen felt better walking around on Saturday than he did the last few days, but he still was limited to rehab and therapy. The Tigers aren't ruling out him making the playoff roster, but his return is looking more likely for sometime during the playoffs than before.
"I don't know. We'll see how next week goes," Guillen said. "But I feel better today."
The Tigers are 19-16 against the AL East this season.
The Tigers are 64-20 when they score first.
Thirteen of the Orioles' last 19 games have been decided by two runs or fewer.