New York Mets' starting rotation issues keep on deepening. Veteran arm Kodai Senga, who was expected to head back to the team's rotation after his brief rehab stint, has informed the team that he is currently not ready to pitch in the MLB.Kodai Senga had a strong start to the season, pitching to a 1.47 ERA in 73.2 innings pitched through early June. However, a hamstring injury put him on the shelf for a month, and the Japanese flamethrower was unable to retain the same early-season form. The Mets manager was questioned about Senga's health in this regard."We're asking the same thing," Mendoza said. "Healthwise, he's 100 percent fine. There's no issues with him. He's not favoring anything. We just haven't been able to help him, whether it's mechanicals or execution, whatever the case might be here. But we haven't gotten there yet. So this is where we're at. But physically he's fine."Senga's first start with the Syracuse Mets of Triple-A was a strong one, earning just 1 run over 6.0 innings on 3 hits and 0 walks with 8 strikeouts. But on Thursday, he was chased early in the game after just 3.2 innings with 4 earned runs."Stuff-wise, [he] was down," Mendoza said of Senga's outing on Thursday. "Whether it was the velo, execution, the secondary pitches were not sharp. So that's the report that I got. And then, watching film, you could see it."And that's probably one of the reasons he's asking for one more time to face hitters, just to kind of continue to work through those issues. So that's what we saw."This is the second consecutive season where Senga has delayed his start. Last year, due to a persistent shoulder injury, the Mets pitcher took the mound only in July. He strained his calf in that outing and didn't come back till the postseason. Even in the playoffs, he was reduced to just three appearances, two as an opener and one from the bullpen.Kodai Senga's unavailability raises doubts on his Mets' postseason participationKodai Senga was expected to lead the Mets' starting rotation in the postseason, but his unavailability might prompt Mendoza and the management to keep him out of the postseason 26-man roster."I think we'll have the conversation and we'll take the 13 guys that we feel are going to give us the best chance to win baseball games in October," Mendoza had said. "I think the biggest thing for him [is] to go out there today and have a good performance. And then we have decisions there."The Mets have had to turn to rookies as starters, like David Peterson, Clay Holmes, and Sean Manaea are winding down towards the end of the season. Senga will face live hitters as the minor league regular season is over, and a decision will be made about his start in the series against the Miami Marlins next week.