"It hurts," Marquis said. "If it was getting progressively better from start to start, then I wouldn't need to be pushed back."
That means the matchup between Marquis (12-6, 3.49 ERA), the National League leader in wins, and Giants standout Matt Cain will not happen. Righty Jason Hammel (5-4, 4.26 ERA) instead will take the mound in the opener of three games against the top two teams in the NL Wild Card race.
The Rockies entered Wednesday atop the Wild Card standings and in second place in the NL West, a half-game ahead of the Giants.
Marquis pitched through the issue for eight innings and gave up one run on five hits while beating the Padres, 6-1, on Sunday. But Rockies manager Jim Tracy said Marquis had to change his grip on some pitches. Marquis pointed to his sinker and changeup, essentially 60-75 percent of his pitches during any given start.
"His finger is on the good side of where we want it to be, yet we're still in the lingering area to where if he goes out there and pitches on Friday, he could tear that thing up again," Tracy said. "We are running the risk of putting ourselves in a position to have him dragging it around with him for, who knows, potentially the remainder of the season, very definitely through the month of August."
The finger was an issue during Marquis' worst start of the season, on June 24, when he gave up eight runs and nine hits in 3 1/3 innings of an 11-3 road loss to the Angels. But it healed, and he threw a complete-game, two-hit shutout against the Dodgers, 3-0, on June 30, and pitched eight scoreless innings of a 1-0 victory over the Nationals on July 6.
Marquis said the problems began after a June 13 start against the Mariners, when he gave up one run in seven innings. He took a no-decision in the Rockies' 5-3 win.
"I woke up at five in the morning that night after the game, and it was just throbbing," Marquis said. "From that point on, I've been battling it."
The finger has bothered him in his past two starts -- a 4-3 loss to the Braves when he went six innings and gave up three runs on seven hits on July 11, and the Sunday start against the Padres.
"The start that he took against Atlanta, I would describe it [the finger] as close to raw," Tracy said. "That may have had something to do with the six innings that he pitched. It wasn't one of his better performances. It was one of his gutsiest performances of the year. He went six innings and we were still in the game, very much in the game, when he left."
The move means the Rockies left-hander Jorge De La Rosa will start Saturday and righty Aaron Cook will pitch Sunday to complete the series with the Giants.
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.