BOSTON — Here’s what we know about Jacoby Ellsbury:

He will continue to get regular playing time in left field until Manny Ramirez (strained oblique muscle) has been cleared to return to the lineup.

And why not?

“The kid has impacted every game he’s been in,” said manager Terry Francona yesterday afternoon. That came, it should be noted, before Ellsbury sliced a double inside the third-base bag in his first at-bat, extending his hitting streak to five games, and added a sacrifice fly in his third.

He will part of the team’s 25-man playoff roster.

Ellsbury wasn’t on the major-league roster before Sept. 1, but because he was in the organization, the Red Sox can have him take the place of someone on the disabled list. Brendan Donnelly and Matt Clement represent available spots.

What we don’t know about Jacoby Ellsbury, of course, is what sort of role he will play in October.

Initially, the Sox planned to include him on their playoff roster to provide speed off the bench and late-inning defense for Ramirez in left.

But Ellsbury’s contributions in the last week, coupled with the paltry offensive output from J.D. Drew, has introduced a new question into the discussion.

To wit: If Ellsbury continues to impress and Drew continues to struggle, would the Red Sox consider playing the rookie over the veteran in right once the playoffs arrive?

Of course, that’s not a question the Red Sox are willing to answer with the playoffs still more than three weeks away. Yesterday, Francona wouldn’t even commit to keeping Ellsbury in the lineup for the foreseeable future.

“Probably,” he said when asked about Ellsbury’s continuing presence in left in Ramirez’ absence, “ but I don’t feel like I have to give the lineup ahead of time. I think it’s fun for (reporters), fun for the fans to get caught up in what can be, what could be, what would be. I don’t need to do that because it just doesn’t help. So, a week from now is a long time.

“If you’re asking me if I like what he’s given us, yeah. But I don’t need to make up the lineup too far ahead.”

If next week constitutes “too far ahead,” for Francona, then surely October represents the afterlife.

Still, it’s impossible not to ponder.

Any suggestion that the Sox wouldn’t sit Drew — and his $70-million contract — was disproved when the Sox actively pursued Jermaine Dye at the trading deadline and went so far as to guarantee Dye five days per week of playing time. Obviously, much of that would have come at Drew’s expense.

Ultimately, the Sox backed off the deal when the Chicago White Sox’ asking price was prohibitive. But by virtue of the serious discussions between the teams, the Sox’ dissatisfaction with Drew was made known.

Five weeks later, Drew continues to founder at the plate. Though he knocked in a run last night — giving him five in his last 22 games and just 49 for the season — he was hitless in four at-bats and is hitting .197 (13-for-66) in the last 21 games.

Worse, Drew took a .384 slugging percentage into last night’s game and hasn’t driven the ball consistently all season. Incredibly, it’s been more than four months since his last homer at Fenway.

On paper, power would seem to be the one advantage Drew would have over Ellsbury. In reality, Ellsbury has more homers (two) in the last five games than Drew has since the end of June.

Drew is a more experienced right fielder, and to be fair, his play there this season has been well above-average. Ellsbury’s professional experience in right is scant, but he played there often in college and there’s no reason his athleticism can’t cover for his lack of familiarity.

If Drew isn’t going to produce runs — and there’s nothing to suggest that he’s got a hot streak coming — how much of a gamble would Ellsbury be?

The rookie has demonstrated a quiet confidence and hasn’t looked the least bit intimidated by his surroundings or the circumstances under which he’s playing. If Ellsbury can take the place of Manny Ramirez in the midst of a playoff run, he surely could take the place of Drew in the postseason.

After all — and this is more an indictment of Drew than it is of Ellsbury — how could he possibly be any worse?

smcadam@projo.com