Happ, Blanton and 37-year-old Pedro Martinez are all strong candidates to start Saturday in Colorado.
Manuel refused to name a starter before Game 2 and said he likely wouldn't name one until after Philadelphia's workout Friday at Colorado.
The brief outing against the Rockies could prove costly for Happ. He was knocked out of the game after he was struck in the left leg by a line drive in the seventh inning.
Happ faced only one batter as Rockies pinch-hitter Seth Smith hit a hard shot straight off Happ's leg for an infield single. The Phillies trainer immediately came rushing out and Happ left the game for Scott Eyre.
Happ sustained a lower left leg contusion. X-rays were negative. Happ went 12-4 for the Phillies this year and made 23 starts. He relieved Blanton, another member of Philadelphia's rotation who was used in relief. Happ, a strong candidate for NL Rookie of the Year, did make 12 relief appearances earlier this season before he was moved into the rotation in place of a struggling Chan Ho Park.
Blanton, a right-hander, went 12-8 and all 31 of his appearances were starts. Blanton threw only 19 pitches in one inning against the Rockies; Happ just four. It was about the equivalent of a bullpen side session, leaving open the chance each of them could come back on Saturday.
Happ struck out 10 and tossed a shutout against the Rockies in July. Blanton did not face the Rockies this season. Blanton's relief appearance was his first since the 2006 postseason with Oakland.
And what about Martinez? Considered finished after he didn't re-sign with the Mets, Martinez was the late-season free-agent steal of the year with a 5-1 record and 3.63 ERA in nine starts. The aging right-hander only pitched seven innings combined in his last two starts, and hasn't taken the mound since a no-decision against Houston on Sept. 30.
"I'd say he's capable of going out there and throwing definitely 90 to 100 pitches," Manuel said. "I can see Pedro getting in a game."
His age, minimal work the last few weeks, and the frigid temperatures expected at Coors Field could rule out Martinez. Manuel said the weather could play a role in his decision.
The Phillies haven't named a starter for Sunday's Game 4, either. It could be one of the losers of the Blanton-Happ-Martinez jumble, or the Phillies could go back to Game 1 winner Cliff Lee on three days' rest.
The Phillies were counting on Hamels to pick up where he left off last postseason when he went 4-0 and was MVP of the NL championship series and the World Series.
He labored on the mound at the same time his wife, Heidi, went into labor with the couple's first child. Hamels said this week his wife was due "any day."
So is a decision on the Game 3 starter.