Adam Thielen's career is nearing the end, but the 35-year-old wide receiver has a new beginning with the Pittsburgh Steelers.

Thielen, a 12-year veteran, joined the practice squad this week after being claimed off waivers from the Minnesota Vikings. Now, Thielen is trying to learn a new offense with just five games remaining in the season.

"At this point, just really focused on what I can control, and that's learning this playbook as fast as possible," Thielen said after practice on Thursday as the Steelers continued to get ready for their game on Sunday against the Ravens in Baltimore. "I want to make an impact today. I'm not even worried about Sunday right now. I want to make an impact today by being mentally and physically prepared. And then at the end of the day, I'm a big believer that you've got to go prove it every day."

Thielen has earned the right to feel at least a little bit entitled. After all, he is a two-time Pro Bowl selection with 693 career receptions. Yet that is far from Thielen's mindset.

"You can't show up somewhere and just be given an opportunity," Thielen said. "You have to go prove what you can do, how you can make an impact, so then they believe in you and trust in you and can give you those opportunities. So, for me, it's just going out there every day like I'm a rookie minicamp tryout guy and trying to prove what I can do, and whatever they see that fit is, I'm ready for it."

Even for someone like Thielen, there can be pressures in coming to a new team, especially one contending for a playoff spot. The Steelers and Ravens are tied for the lead in the AFC North, and first place is on the line on Sunday.

"I've got to prove it to myself first," Thielen said. 'In the classroom, just being really confident and knowing my stuff, knowing the different checks, knowing the different alerts. I think just making sure that they're comfortable with what I know and how well I know it, and then see what happens."

It is unclear if Thielen will be promoted to the 53-man roster or at least be elevated from the practice squad for Sunday's game. He was barely a factor for the Vikings this season, catching eight passes on 18 targets for 69 yards in 11 games.

However, the Steelers have been looking for a second reliable wide receiver to pair with DK Metcalf all season. Metcalf has been a disappointment since being acquired from the Seattle Seahawks in an offseason trade and signing a five-year, $150-million contract. The two-time Pro Bowler has just 45 receptions for 605 yards and five touchdowns.

Defenses have often double-teamed Metcalf, though, because the Steelers lack a good WR2. Calvin Austin III has just 26 catches for 278 yards and two TDs.

Can Thielen be the second threat that the Steelers can pair with Metcalf? It seems like a long shot, but Thielen is going to give it his best shot.

"Thankful that I've got a lot of great teammates that are staying after (practice) and walking through those plays with me and talking, both the backup quarterbacks just going through a bunch of stuff with me has been fantastic and really starting to feel more comfortable," Thielen said. "Every time I get those walkthrough reps makes me feel more comfortable."