For John Lannan, this whole “On The DL” thing was a whole new animal.

“This is my first time on the DL,” said the 28-year-old lefty by his locker in the clubhouse at Citizens Bank Park on Thursday, about an hour and a half after the Phillies put him on the 15-day variety with a strained left quadriceps tendon.

But for the organization, replacing an injured player on the roster is nothing new. And with the apparent severity of Lannan's injury, their decision can’t make them look like they are.

“It's a fairly serious injury,” GM Ruben Amaro said Monday. “I know John was upset about it, but there’s not much you can do other than rehab it and come back as soon as possible.

"One of the things we want to be cautious about is pushing it and having him rupture it.”

Amaro said they won’t decide on Lannan's replacement in the rotation until next Monday, Lannan’s next scheduled turn.

Until then, he said, they'll fill out the roster with a reliever, to provide Charlie Manuel with another bullpen option for this four-game set with the Cardinals.

Come decision time, Amaro's top minor league starting options are Jonathan Pettibone, Adam Morgan, Ethan Martin, and Tyler Cloyd, all currently in Triple-A.

“We have a few options there,” he said. “We're kicking them around right now.”

Cloyd, 25, earned a big league callup last September with a 12-1 mark and 2.35 ERA in 22 starts in Triple-A last season. When he’d arrived, he went 2-2 with a 4.91 ERA with 8 home runs in 6 starts.

Of those yet to make their big-league debuts, Pettibone, 22, entered 2013 the most experienced, from a grand total of 7 games above Double-A. Through 2 starts this year, the righty is 0-1 with a 9.64 ERA and 8 strikeouts to 5 walks.

Martin, 23, the Phillies’ haul in the Shane Victorino trade with the Dodgers last July, is 1-0 with a 4.82 ERA through his first two starts of the minor league season.

Morgan, 23, impressed during camp this year, in particular with that spot start after Roy Halladay was sent for minor league work, going 4 2/3 scoreless against the Braves on March 22. That’s continued early for him in Triple-A, where the lefthander is working a 1-0 mark and 1.29 ERA in his first 2 starts.

Only, Morgan pitched on Thursday, four days from Lannan’s next turn.

Amaro was asked if Morgan is out of the question, then.

“He probably would be. I’m not sure we want to bring a kid back on short rest. It probably doesn’t make much sense.”

But Amaro said nothing is guaranteed for the first man to get the call.

“Again, we're trying to assess who we're going to bring for the first and then kind of go from there,” he said. “We’ll see how that person performs and if that person performs well then we'll stay with them. A lot of it depends on how that guy throws and we'll kind of take it one day at a time on that.”

Amaro was asked if starting Raul Valdes, as they did in last July's "bullpen game" was an option.

“That’s a possibility we’ve kicked around,” he said. “But it’s probably not what we want to do.”

He was also asked about outside moves. He said: “We could, but we probably won’t."

He was even asked about bringing up Darin Ruf for four days instead, before selecting his starter.

“We’ll bring Ruf up when we think he’s ready to help us contribute,” he said. “Right now, he’s still getting acclimated to playing left field. If there was something that happened to (Domonic Brown), he probably would have been a candidate to come, but Brownie is OK.”

If there’s a silver lining, it’s that these four days could present the organization with options for its flailing bullpen, the owners of a fourth-worst-in-baseball 5.01 ERA.

Justin De Fratus, 25, Cesar Jiminez, 28, Joe Savery, 27, and have yet to allow a run in 18 1/3 innings spanning 12 appearances out of the Lehigh Valley ‘pen.

Jake Diekman, 26, has a 5.79 ERA in 4 2/3 innings spanning 5 appearances.

Though, it is early.

“Yeah, just like there’s too much weight on the numbers here right now,” said Amaro when asked about the youth of the year. “Here too. We’ve played 15 games. Somebody said we still have 90 percent of the season left.”

Still, early becomes late in a hurry. And in the meantime, the Phillies can't afford to miss on Lannan's replacement, whoever and however many hes there may be.