So the attention has turned to who will start at the other cornerback position opposite him for the San Francisco 49ers in their season opener against the Minnesota Vikings on ESPN's Monday Night Football in six days.
"[They] are right there right now, really getting after it," Tomsula said Tuesday. "Now Dontae [Johnson is also] in the mix.
"You will see, throughout the year, matchup-wise, you'll see us matching up the way we need to match up, with those guys, between those three."
Left out of the conversation was four-year veteran Shareece Wright, one of the more high-profile free-agent signings the Niners made this offseason. He opened the preseason starting opposite Brock.
Acker picked off Peyton Manning in the end zone in the preseason and broke up another potential Manning TD pass while Reaser, a younger cousin of late Washington DB Sean Taylor, also saw first-team reps in camp.
Johnson, at 6-foot-2, 200 pounds, is the most physically imposing cornerback. Wright has but one interception in his career and his 12 pass interference penalties since 2013 to lead the NFL in that time frame.
Then who would seemingly be the clubhouse leader? Tomsula was not biting, though he may have tipped his hand.
"But Acker's really come on and done a great job, if you want somebody that's going to be on a depth chart, it will probably see Reaser and Acker," Tomsula said. "Acker's done a great job but Reaser is in the mix."
Both had "redshirt" years as rookies last season, Reaser dealing an ACL injury and Acker with a foot issue.
"Those guys have dealt with some injuries their rookie year but they've come, man, they've come miles since then," free safety Eric Reid said late in training camp. "Acker in particular this offseason, he looks like a different person. He's running around, explosive, making plays, he's building a case for him[self], and that's good."
And about Brock and his hamstring?
"Fine, great," Tomsula said. "I don't think he's going to show up on any injury reports."