Receiver Anthony Armstrong, who joined the Dolphins last weekend after the Redskins waived him, said he has picked up the offense well and expects to play Sunday at Houston.

“I have a firm grasp on the game plan,” he said. “I know what I need to know to contribute.”

Coach Joe Philbin said Armstrong “has caught the ball well in practice. He seems to be a bright guy, seems to have a pretty good awareness for a guy who just got here a couple days ago. I’m hopeful he can contribute in some fashion.”

Armstrong is in the unusual position of having already been a teammate of two of the ballyhooed rookie quarterbacks — Washington’s Robert Griffin III and the Dolphins’ Ryan Tannehill.

“Robert has Olympic athleticism,” Armstrong said. “He has a lot more pressure on him than Ryan. Both have strong arms. Robert’s [deeper] passes have a lot of zip. Ryan’s a little more catchable, but they’re asked to make different throws. Both will do well.”

Though he wasn’t making a comparison with Griffin, Armstrong likes that Tannehill does not leave his receivers in especially vulnerable positions. “If a linebacker is on you, he will throw it to your back shoulder so you don’t take a [direct face-to-face] hit,” Armstrong said.

Injury Report

Defensive tackle Tony McDaniel (knee/toes) was listed as questionable on Friday’s injury report. Jake Long (knee), John Jerry (ankle), Brian Hartline (calf), Koa Misi (back), Derrick Shelby (shoulder) and Jason Trusnik (ankle) were listed as probable.

The significant news from Houston’s injury report was running back Arian Foster being listed as questionable with a knee injury.

Coach Gary Kubiak said Foster is a game-time decision, but Foster told Houston media that he will play.

Linebackers Brooks Reed (hip) and Bryan Braman (hamstring) were also listed as questionable.

Fins’ 4th CB

The Dolphins have only four cornerbacks on the roster, and the fourth is R.J. Stanford, who was claimed off waivers when Carolina cut him last weekend.

Asked if that concerns him, Philbin smiled.

“In a perfect world, your fourth corner would have been with you longer and have more repetitions,” he said. “We like what we’ve seen so far. We feel he’ll be ready to contribute if needed.”

This and that

• The Dolphins kept their cornerbacks on the same side of the field last season, and if Miami does that again, 6-3 Sean Smith would not cover Houston’s 6-3 Andre Johnson. Richard Marshall, who is 5-11, would get that assignment instead. But Philbin suggested he’s willing to change that approach.

“I’m not opposed to moving a guy around,” he said. “It’s totally fluid, all depends on how we feel about the matchups, how much movement we anticipate [from opposing offenses].”

If Marshall covers Johnson, he likely would get help from a safety.

• Philbin acknowledged that adding safety Troy Nolan, who was cut by Houston last Friday, gives Miami “some benefit” competitively against his former team, “but I don’t know that it’s going to have a huge impact on the game. They may change up a signal or two. It might be different if their secondary coach came over this week and we traded coaches.”

• The Dolphins practiced Hail Mary passes Friday, and Chris Clemons knocked down one of them, but unfortunately for the defense, right into the hands of Legedu Naanee for a touchdown.