"I want it to be better," said Spencer after a practice Monday that he didn't participate in. "Being injured is discouraging."
Spencer said if he undergoes surgery he will be out from two-to-three weeks. Team officials are still monitoring Spencer's health and haven't made a final determination regarding surgery.
Spencer aggravated a bone bruise in his left knee that kept him out of parts of organized team activities and minicamp and the last hour of Sunday's practice and the entire Monday session.
Spencer said the pain started in Saturday's conditioning run. He went through the early part of Sunday's practice but did not take part in any team drills. He had an MRI on Sunday night, which confirmed the bruise.
"We don't think it's severe," Cowboys coach Jason Garrett said. "We'll just come up with what we think is the best option here in the next few days."
Any prolonged absence for Spencer would hurt a defensive line that lost end Tyrone Crawford for the season with a torn Achilles suffered Sunday. Crawford will return to Dallas for surgery later this week. Because of league rules, he will not be placed on injured reserve until Aug. 27, when teams cut rosters to 75 players.
The Cowboys have an open roster spot with Josh Brent's recent retirement, but will look internally before going out for any free-agent help.
Defensive tackle Jay Ratliff is on the active/physically unable to perform list with a strained hamstring and is not practicing.
"At some point we need to reload a little, but on the defensive line," Garrett said.
Crawford suffered the injury in non-contact pass-rush drills, collapsing to the ground as he went through a line of dummies. Teammates expressed disappointment for the second-year defensive end, whom the Cowboys were viewing as a top-end rotational player in their new scheme.
Without Crawford and Spencer, Kyle Wilber, who did not play much last season as a rookie, started opposite DeMarcus Ware on Monday. The second-team defensive ends were Monte Taylor and Cameron Sheffield.
"It hurts," defensive tackle Jason Hatcher said of Crawford. "He's like a little brother to me, came over to the house, hung out, picked my brain, asked questions. When a young guy like that goes down like that that's close to you it hurts. At the same time we know what's at stake. We've got to keep playing and get there for him."