Cardinals tackle Jared Veldheer (68) helps up quarterback Carson Palmer after a play Monday night.

Questions surround the Cardinals' offensive line.

It's too early to know if injured tackle D.J. Humphries (knee) or injured guard Mike Iupati (triceps) will play this week against San Francisco because coach Bruce Arians first wants to see them in practice. Guard Alex Boone and tackle John Wetzel, the guys filling in for Iupati and Humphries, both underwent MRIs Tuesday after hurting pectoral muscles.

Meanwhile, Arians is looking for better protection throughout the line, and all the Cardinals are hoping tackle Jared Veldheer can return to form.

The veteran, who is playing the right side this season after a career spent at left tackle, was the most prominent

day-after topic Tuesday after he struggled for a second straight game.

"It's technique. Just technique," Arians said in assessing Veldheer. "Same problems he had in the left side, being bull-rushed and not getting his hands up. Got to get his hands on people. He gets his hands on people, he's big and strong, won't get bull-rushed."

Veldheer was excellent in 2014 after signing as a free agent. He took a step back in 2015, and he went into last season having changed his body in order to regain some strength. He only got to play half the season before injuring his triceps. Humphries, who had been the right tackle, took Veldheer's spot.

In the offseason, and with an eye on the future, the Cards decided to keep Humphries on the left and move Veldheer to the right. The transition continues to be difficult.

"It's not easy," Veldheer said after Monday's game. "I just continue with the mindset of pushing through that wall, breaking through. I wasn't able to do that tonight, but I'm going to look at this film with everything I have and attack practice, and keep pushing forward, trying to be the best I can be."

Arians said he had no concerns whatsoever that Veldheer's brief contemplation of retirement in training camp was impacting Veldheer's play. The coach has given no thought to making a change with right tackle.

"I don't know where you change to," Arians said. "What's behind door number two? A rookie? He's got to do his job."

As it is, rookie Will Holden would have to play tackle if both Humphries and Wetzel can't play Sunday.

Arians said Boone played well Monday, and he was satisfied with center A.Q. Shipley. Wetzel "held his own." Veldheer and right guard Evan Boehm – whom Arians said was still learning – were the biggest issues.

"We have to protect better," Arians said. "There's no questions how to do it. You just have to do your technique and block your guy. It's not scheme, it's one-on-one football."

ELLINGTON EMERGES, BUT JOHNSON STILL THE STARTER

Arians said the Cardinals "left the run probably too soon" against the Cowboys. The Cards ran 21 times

(compared to 48 passes) for 49 yards, only 2.3 yards a carry. Andre Ellington looked the best with his 22 yards on five tries. Starter Chris Johnson had just 17 yards on 12 attempts, and Arians said "I thought Chris looked rusty."

Arians said he hoped that Johnson's rust would be gone going forward. The coach said during an appearance on Arizona Sports that Johnson would remain the starter at running back against the 49ers this week, with Ellington in the third-down role and Kerwynn Williams continuing to pick up carries here and there.

Ellington could end up seeing increased work, however, regardless of situation. "When he was our guy (in 2013 and 2014), he had 80-yard runs up the middle," Arians said. "We're not a perimeter running team."

TOO QUICK OF A CHALLENGE

Arians took the blame for the bad challenge on J.J. Nelson's near-catch on the sideline. Replays clearly showed Nelson lose the ball as he hit the ground. Arians said he was so caught up in whether Nelson's feet were in – and how the officials waffled on the call – that he jumped in too soon.            

"I challenged it because (the officials) told me he caught the ball but his feet were out, lead official said his feet were in, and I challenged way too fast because upstairs the ball came out," Arians said. "That's on me, not listening to the guys upstairs."

PRACTICE-SQUAD ADDITIONS

The Cardinals signed TE Anthony Denham Jr. – most recently with Philadelphia -- and LB Earl Okine – most recently with Detroit - to the practice squad. There were two openings after TE Ricky Seals-Jones was promoted to the active roster and the Packers signed away T Ulrick John.