PHOENIX -- Frank Francisco appeared to be zeroing in on a return to active duty before another setback Saturday thrust the closer's status in doubt.

Scheduled to pitch for Double-A Binghamton, Francisco did not appear in the game, later telling the Binghamton Press & Sun-Bulletin that he felt soreness in his left side and intended to pitch on Sunday. Mets manager Terry Collins had not been briefed on the injury as of Saturday evening and could not comment on its severity.

Earlier in the day, Collins said that if all went well in Francisco's outing for the B-Mets, it could be his final Minor League rehab appearance. Initially expected to miss no more than 15 days, Francisco suffered a similar setback earlier this month, then received an injection for an unrelated knee ailment last week.

On the disabled list since June 23 with a strained left oblique, Francisco struggled in his rehab debut for Binghamton, but settled down to notch a scoreless save on Friday. Though interim closer Bobby Parnell has been shaky at times in Francisco's absence, blowing two saves in five chances, he has also posted a 2.31 ERA with more than a strikeout per inning over that span.

Francisco was one of the team's best relievers prior to landing on the disabled list, converting 10 of his last 11 save opportunities with a 1.76 ERA.

Collins plans to keep Bay in lineup every day

PHOENIX -- This is not a platoon -- at least not yet. Despite outfielder Jason Bay's season-long slump and 0-for-15 funk entering Saturday's play, and despite the presence of tough D-backs right-hander Ian Kennedy on the mound, Mets manager Terry Collins plugged Bay back into Saturday's lineup, batting sixth. The goal is to give Bay as many at-bats as possible as he works through his troubles.

"He's going to be in there," Collins said, noting that Bay will also play Sunday against lefty Joe Saunders. "He's the answer to what we're trying to find, and that's that big right-handed bat. If you sit him down ... he's not going to get better."

To be certain, Bay's leash will not last indefinitely; injured outfielder Mike Baxter is due back from the disabled list within days, and could start infringing upon Bay's playing time shortly thereafter. Given Baxter's strong play earlier this season, it is not inconceivable to think he could force Collins to utilize a left-field platoon before long.

So Bay, who entered Saturday just 4-for-31 since returning from the DL, must right himself quickly if he intends to keep a stranglehold on the job. Bay's most significant problem, according to Collins, is the simple fact that injuries have prevented him from stringing together any consistent run of at-bats. Once he does that, Collins said, he should find himself in a better position to produce.

"You continue to watch him take batting practice and stuff, and he continues to show you that the power's still there," Collins said. "Now it's just a matter of making sure mechanically, he gets his feet on the ground, he gets in the correct position to attack the baseball.

"It's not for lack of effort that he's not hitting."

Since signing a four-year, $66-million contract with the Mets prior to the 2010 season, Bay has hit just .242 with 23 home runs in 1,028 plate appearances. He is still guaranteed $19 million after this year.