Spencer has not practiced since July 25 but has always said he would be able to play in Sunday's season opener against the New York Giants and remains cautiously optimistic.
"It's really hard for me because I love being out there and stuff like that," Spencer said, "but at the same time, I just got to listen to my body and do what it tells me to do."
Spencer said it is possible he could practice Friday depending on how his knee felt after running Thursday. He said the swelling subsided and believes he is seeing progress.
"I wanted to play in this game, so I expected to do some stuff on Wednesday and I wasn't able to do that," Spencer said. "It's not really where I wanted to be at right now."
If Spencer cannot play, George Selvie would make the first start of his career. The Cowboys traded for two defensive ends recently in Edgar Jones (Kansas City) and Caesar Rayford (Indianapolis) and could use multiple players to replace Spencer against the Giants.
Even if Spencer can play, it is doubtful he would see full-time action.
"If I can go out there, I want to be able to do the things that I'm able to do when I'm healthy," Spencer said.
Defensive tackle Ben Bass was added to the injury report with a shoulder injury and was limited. Running back Lance Dunbar (foot) and safety Danny McCray (hamstring) missed their third day of practice this week. Guard Ronald Leary (knee) was a full participant in practice.