Updated JUL 28, 2014 4:54p ET  GLENDALE, Ariz. -- Cardinals offensive lineman Bobby Massie doesn't have to be told what's at stake in his third NFL training camp. He knows plenty well himself, and from the way he's talking early in training camp, he's fired up about it.  "I've got an opportunity to showcase what I can do," Massie said. "Basically, it's my spot to lose.  A former fourth-round pick who has seen his share of ups and downs, Massie has the opportunity to be a critical piece to the Cardinals' rebuilt offensive line and enters the contact portion of training camp the strong favorite at right tackle.  Cardinals coach Bruce Arians used the same words as Massie when discussing the situation at right tackle: "His job to lose."  But there's a lot of training camp left, and Arians says no one is "starting" yet.  Massie has shown through the spring and first couple days of training camp he has a greater understanding of what he must do to win his job and keep it.  "I don't even think he was on the (mental error) sheet today from Saturday," Arians said Sunday. "That was a big step for him."  Massie represents half the unsettled right side of the Cardinals offensive line. The left side is essentially set with free agent left tackle Jared Veldheer and left guard Jonathan Cooper, who missed last season, his rookie year, with a broken fibula. Veteran Lyle Sendlein remains the line's anchor at center.  At right guard, second-year Cardinal Paul Fanaika holds a lead on 2013 fourth-round pick Earl Watford, and like Massie, the spot -- per Arians -- is his to lose. But Massie is the piece the Cardinals so much want to see thrive after an apparent regression last season.  Massie appeared to turn the corner in 2012. He did not allow a sack in the second half of the season after allowing 13 through the first eight weeks. But in 2013, Massie didn't start.  "I finished a top three tackle in the league in pass protection, and I was still kind of coming off that high," Massie said. "I felt like I deserved the spot because of the way I played, but obviously that wasn't the case and that showed. It was a learning experience for me."  Massie spent the year backing up Eric Winston, whom the Cardinals signed early in training camp, and learning Arians' offense, which he admitted was difficult in the time frame the team expected. In total, Massie saw action in just nine games after starting 16 in 2012. Needless to say, he had plenty of motivation entering the offseason.  In the spring, Massie worked to eliminate the mental errors that plagued him the previous two seasons. Arians' observation suggests he progressed there, and Massie feels he has at the same time progressed physically.  "I feel like this is the best shape physically and mentally I've ever been in -- high school, college, whatever," Massie said. "This is my year to showcase what I can do.  "No pressure. I put myself in this position so the only person that can mess it up is me."  Fanaika takes the same approach to his position at right guard, where he started every game last season and is holding off Watford early in camp.  "Competition is what drives you to get better," Fanaika said. "You just have to welcome the challenge, go out there with the right approach, work on your craft and get better every day. If you know what you're doing, you're going to be depended on."  Arians said Watford is legitimately competing for the guard spot, and Bradley Sowell is doing the same behind Massie. Neither spot has been decided, and the competition could start to get interesting with the Cardinals now practicing in pads, but Arians says there won't be any shuffling unless the competition warrants it.  "The competition is still alive, but the other two guys are behind just because the other two guys won't let them take the job yet mentally," Arians said. "Physically, that's a whole different ball game."  Follow Tyler Lockman on Twitter
Right tackle is Bobby Massie's job to lose, and his keeping it will help secure the rebuilt line