The injury will likely keep Roethlisberger from fully participating in practice Wednesday, but not from playing on Sunday against Philadelphia.
The Steelers said last week that their quarterback was nursing a sore shoulder, but a TV commentator on Sunday night termed the injury a shoulder separation.
During his weekly news conference Tuesday, Tomlin appeared agitated by the latter description.
"I have no idea where that report came from," Tomlin said. "It didn't come from me or my medical staff. If anybody in here has got any information about where that report came from, send them to me."
Tomlin said Roethlisberger sprained his AC joint, an injury to the ligaments that attach the collarbone to the shoulder blade.
Asked if Roethlisberger was the source of the disputed information, Tomlin said, "Not to my knowledge."
The issue may be one of semantics. The American Academy of Orthopedic Surgeons describes a mild shoulder separation as a sprain of the AC ligament. It differs from more severe shoulder separations in which the ligament is torn.
Whatever the injury, Roethlisberger threw for 186 yards and a touchdown during Pittsburgh's 10-6 win over Cleveland on Sunday and is expected to play this Sunday against the Eagles.
"He said it feels better than it did a week ago, which is good," Tomlin said.
Roethlisberger was sacked three times Sunday but perhaps endured his hardest hit -- from 350-pound Browns defensive tackle Shaun Rogers -- after releasing the ball. Roethlisberger appeared to hold his arm gingerly after that play.
Tomlin said Roethlisberger can do no further damage to the shoulder by playing. The coach was asked if it was a worry that his quarterback was missing so much practice time.
"It really depends on the quarterback," Tomlin said. "Some guys require a great number of snaps to get prepared to play. Some guys can learn visually, film room and so forth. Thankfully with Ben he's a pretty quick study and sharp guy. ... It doesn't take him a great number of reps to be prepared to play.
"Hopefully it won't be an issue this week. I know it won't be an excuse."
In other injury news, defensive end Brett Keisel has a calf strain. He is out for the Eagles game and likely for at least a month overall, though Tomlin said he would be evaluated "week to week."
Travis Kirschke is expected to take his place in the starting lineup, with veteran Orpheus Roye being added to the active roster Sunday so he can join the team's six-man rotation on the defensive line.
Also, starting cornerback Deshea Townsend's heel contusion might force him to miss his second game in a row.