Ted Lilly’s most glaring fault Monday night wasn’t getting shelled for three innings before having to exit a 12-2 loss to the Rockies with back pain. It was the silence the Dodgers starter maintained about tightness in his back since making his first start of the season five days earlier.

Dodgers manager Don Mattingly was none too pleased to discover after the series opener against the Rockies that Lilly, who began the season one the disabled list due to left shoulder labrum surgery, hadn’t informed the Dodgers training staff of his ailment following a five-inning outing against the Mets a week ago in which he only allowed one run.

“He can’t just keep that to himself,” Mattingly said. “Then at least we know going in to the game that we possibly should have a guy that can go four or five innings, instead of having to use the whole group.”

Following Lilly’s exit, the Dodgers used a total of five relievers over the final six innings.

“The frustrating part was, if you’re feeling it before you go out there and you don’t tell anybody,” Mattingly said, “then for us it’s like, let us make some plans and give us a chance to win.”

Lilly had an MRI on Tuesday, the results of which were unknown as of the beginning of Tuesday’s game. If the severity of Lilly’s injury is enough to keep him from starting Saturday at San Francisco, or worse, make him the fifth Dodgers starter on the disabled list, Matt Magill would likely take his turn in the rotation against the Giants.

“That’s the logical thing to do,” Mattingly said. “But we talked about putting Magill in the pen a little bit.”

In his major league debut on Saturday, the 23-year-old Magill allowed two runs in 6 2/3 innings the day he was called up from Triple-A Albuquerque.