FRISCO, Texas — Tony Romo is out with yet another back injury and it’s unknown when he will return, although Dallas Coach Jason Garrett says he expects his star quarterback to play this season.

Garrett said Saturday that Romo sustained a broken bone in his back when he was hit from behind by Seattle’s Cliff Avrill and slid awkwardly on the third play of a preseason game.

Romo tried to get back into Thursday’s game and said afterward that he was OK. But Garrett said the 36-year-old woke up Friday with stiffness, and an MRI revealed Romo’s fourth back injury in less than four years. The injury will not require surgery.

Garrett wouldn’t rule out Romo for the regular-season opener Sept. 11 against the New York Giants. Rookie Dak Prescott, a fourth-round pick who has had a strong preseason, is the presumed starter, although Garrett wouldn’t acknowledge that either.

“If you guys remember, he has played with fractures in his back before,” Garrett said, referring to Romo’s quick return from a small fracture in his back in 2014.

“So that probably more than anything else is what is not giving us a timetable. We’ve heard a wide range of possibilities in terms of when he would be able to play.”

PATRIOTS: Wide receiver Julian Edelman was rusty in his preseason debut Friday night in a 19-17 win against the Panthers.

There was minimal concern over Edelman’s twice-repaired foot last week when he reappeared at practice against the Bears, as he spun through their defense to the tune of eight receptions in team drills during a dominant day.

But Friday, Edelman’s timing was just off. He had one catch for 6 yards on three targets. This was why it was important for the Patriots to get Edelman some game reps with both Tom Brady and Jimmy Garoppolo before the Sept. 11 regular-season opener.

Garoppolo and Edelman weren’t in sync with their first attempt on the opening series, as Edelman stopped his route to seemingly reverse course when the quarterback fired the ball as though the receiver were continuing his crossing pattern.

It clanked off linebacker Luke Kuechly’s hands for a near interception on third down.

Edelman was then flagged for holding on the first play of the Patriots’ second series, which negated Tyler Gaffney’s 7-yard run.

And when Brady took over on the fourth offensive series, Edelman dropped the QB’s second pass.

Edelman played a limited amount of reps while rotating with the first-team offense, but this was clearly a necessary exercise to get him up to speed with the two signal-callers.

Defensive tackle Terrance Knighton was noticeably stuck on the sideline, and his chances to make the 53-man roster seem to be dwindling.

Afterward, Knighton said he was not told he’d be relegated to the bench against the Panthers.

CHIEFS: Kansas City acquired cornerback Kenneth Acker from the San Francisco 49ers for an undisclosed draft pick.

A sixth-round pick by the 49ers in 2014, Acker missed his rookie season because of a foot injury. He played in 15 games last season and had three interceptions.

RAVENS: Tight end Benjamin Watson tore his right Achilles tendon and is likely lost for the season.

The injury occurred on Baltimore’s first offensive play in a preseason game against Detroit on Saturday.

Watson, 35, appeared to trip while running a pattern and slumped to the turf. After he finally got up, he had to be helped off the field.