With starter Ben Roethlisberger's status for Sunday's game against the Colts uncertain due to his reinjured right shoulder, the Steelers (6-2) may give Leftwich his first start since last Nov. 18 with Atlanta.
A source told ESPN.com's John Clayton, however, that Roethlisberger has a decent chance of being able to play Sunday.
Roethlisberger underwent an MRI exam Tuesday, but the Steelers did not immediately release the results. He reinjured his separated right shoulder on a quarterback sneak near the end of the second quarter Monday night.
Leftwich took over to set up a touchdown with a long completion on his first throw, threw for a score and led another TD drive during a 23-6 win in Washington.
Leftwich's line score for a short but productive night's work: 7-of-10 for 129 yards, no interceptions and one satisfied locker room as the Steelers preserved their AFC North lead.
"He made a lot of friends in there," coach Mike Tomlin said.
The sore shoulder has bothered Roethlisberger, though he hasn't said how much, since he was hurt Sept. 7 against Houston.
"I'm sure his shoulder has affected him," Tomlin said. "How much it has affected him, I don't know. It really is kind of irrelevant. We really don't look for or seek excuses. We don't make them, whether we're talking about Ben or anybody else."
Unless Roethlisberger's injury heals in a hurry during a shortened week of preparation, the Steelers may need Leftwich to bail them out again.
"No, it does not surprise me," Tomlin said Tuesday of Leftwich's ability to come off the bench and throw quickly and effectively. "That's one of the characteristics of Byron. That's who he is. He's a quick decision-maker. ... That's what makes him who he is."
A former first-round pick and starter in Jacksonville, Leftwich spent last season with the Falcons after being cut by the Jaguars.
"He's an experienced player. He's not new to this," running back Willie Parker said. "Nobody was surprised by how well he came out and played. Ben went down and Byron seamlessly came in and did what he had to do."
Leftwich's mobility doesn't match Roethlisberger's, but his arm may be as good or better. Surprisingly, Leftwich was out of the league when NFL training camps opened and signed with Pittsburgh only after former backup Charlie Batch broke his collarbone Aug. 8. Batch is out for the season.
"I truly don't know the offense yet," Leftwich said. "I just got here late in the preseason, so that's what makes it tough."
The Steelers believed they were equipped to handle a Roethlisberger injury with Batch around; he was 3-0 as a starter in 2005 and 2006. They feel the same way with Leftwich, who is expected to seek a starting job elsewhere in the league after this season.
"That's the hardest position, backup quarterback," wide receiver Hines Ward said. "To come into the game after really not taking a lot of reps in practice, he did a phenomenal job. Byron gave us fits down in Jacksonville for a long time, so it's great he can come off the bench with the guys trying to rally around him."
Depending on Roethlisberger's status, the Steelers may have to rally around Leftwich again Sunday.
"He practices every week like he is going to help this team win the next game," linebacker James Harrison said. "He did the job we expected him to do."
Tight end Heath Miller (sprained ankle) is doubtful for Indianapolis (4-4), but Tomlin said safety Ryan Clark (shoulder) could return after missing one game. Tomlin offered no update on left tackle Marvel Smith (back), who hasn't played in a month.
Information from The Associated Press was used in this report.