"We'll just have to make some tough, tough decisions in going forward," Manuel said, "if we deem after his next outing that he's ready to join us and compete at the Major League level."
In recent weeks, Manuel indicated that Maine would almost certainly replace Takahashi as soon as he returned to health.
"We're going to have to sit down and talk about that when the time comes," general manager Omar Minaya said. "Me, Jerry and [pitching coach] Dan Warthen, we'll talk about what's the next step with Takahashi and with R.A. Dickey throwing well. But it's a good problem to have."
Maine, who needed 88 pitches to throw 4 1/3 innings of one-run ball for Buffalo on Friday, sat in the high 80s with his fastball in that outing. He was 1-3 with a 6.13 ERA before hitting the disabled list with a case of right rotator cuff tendinitis last month.
Takahashi, meanwhile, has rebounded brilliantly after two subpar outings, following up a victory over the Orioles last weekend with six shutout innings against the Yankees in Friday night's 4-0 win.
That latter outing impressed Manuel most, considering Takahashi did it against a Yankees lineup that had seen him once before and had studied his tendencies.
"I think he has a tremendous sense for pitching," Manuel said. "He appears to make adjustments like a good hitter during the at-bat."
Maine, who is making $3.3 million this season, has won a combined 18 games over the past three seasons, after finishing 15-10 with a 3.91 ERA in his breakout season of 2007.
Takahashi, meanwhile, is 3-1 with a 3.81 ERA since joining the rotation last month, having struck out 17 batters and walked seven. Dickey has also been a revelation, becoming the first pitcher in franchise history to have at least five wins with no losses in his first six starts with the club.