PITTSBURGH -- The promise of Pittsburgh's pitching future is on display this weekend in a series against Philadelphia.

But that is window dressing that obscures a state of flux in the Pirates rotation.

Rookie Jameson Taillon (2-1, 3.44 ERA) is scheduled to start the series finale against the Phillies. That much is known.

After a day off Monday, the two season-long starters, Francisco Liriano and Gerrit Cole, are slated to pitch against the visiting Mariners Tuesday and Wednesday.

Beyond that?

"We have Taillon (Sunday)," Pirates manager Clint Hurdle said. "We've got Liriano and Cole through Seattle, and after that we'll get back to you."

Promising rookie Tyler Glasnow left his second career start in the fourth inning Saturday with right shoulder discomfort.

Chad Kuhl, another touted prospect, made his big league debut last month. He was pulled in the first inning of a Triple-A Indianapolis game Saturday for reasons that are unclear.

Jonathan Niese and Juan Nicasio are now in the bullpen. Jeff Locke, who has struggled, will skip his turn this week with off days Monday and Thursday but could be available out of the bullpen.

There was no indication of the severity of Glasnow's injury, although he talked of taking things "day to day."

So that leaves Pittsburgh, which unlike Philadelphia, seems like a legitimate contender for a National League wild-card spot to worry only about today.

"That's just what we do. We're professionals," Pirates second baseman Josh Harrison said of his club's resiliency. "You've just got to take care of business and at the end of the day know that it's a funny game and you never know what can happen, so just keep plugging away."

Philadelphia and Pittsburgh have split the first two games of the series.

The Phillies' best pitcher this season, Vince Velasquez (8-2, 3.15 ERA) is expected to start Sunday.

Although he had some arm tiredness before the All-Star break, Velasquez had won his last three starts before the break.

In his only start since, he pitched well but did not earn a decision Tuesday in Philadelphia's 2-1, 10-inning loss to Miami.

"He pounded the strike zone," manager Pete Mackanin said. "I know he had four walks, but he wasn't all over the place, and he had a great changeup today and he had velocity on his fastball with movement."

Velasquez allowed a run on three hits in seven innings, using 105 pitches. He struck out five. It was the first time he made it through the seventh since a 16-strikeout complete game shutout April 14, a 3-0 win against San Diego.

"I was pretty much refreshed," Velasquez told CSNPhilly. "No need to hold anything back."

Velasquez now recorded three straight quality starts. He has allowed five runs in 24 innings (four starts) since returning from the disabled list on June 27.

He's recorded 25 strikeouts with eight walks in that span.