CHARLOTTE, N.C. -- Few outside the medical profession probably understand what Carolina Panthers quarterback Cam Newton faces after undergoing rotator cuff surgery more than Chad Pennington.

The former New York Jets and Miami Dolphins quarterback had two rotator cuff surgeries on his throwing shoulder and four total shoulder surgeries during his 11-year (2000-2010) NFL career.

"I feel like a Ph.D. in this thing," Pennington told ESPN.com with a laugh.

Pennington said Newton's biggest challenge will be mental, understanding the throws he can and can't make, that there may be inconsistencies from one throw to the next, that he may not feel 100 percent until the 2018 season.

"It can play tricks on you with your confidence if you're not careful," Pennington said of the inconsistencies. "The only way I knew how to deal with that was to be sharp mentally and trust my decisions and believe in the decision I was making ... knowing I'm going through a rehab process."

Pennington's first advice to Newton is don't rush the rehabilitation that the Panthers project to take 12-16 weeks, which puts the 2015 NFL MVP's return near the start of training camp.

"It's natural to get competitive with that," Pennington said. "I know I did, and I wish that I didn't. It's a natural thing to try to get competitive with it and beat the rehab times and show you're back.

"I would strongly suggest he takes all the time needed to truly get back to where he needs to get to perform well."

Pennington understands every rotator cuff injury is different, and his two fully torn cuffs in 2005 were different than the partially torn right rotator cuff Newton suffered this past season. Newton's rehab will also be a month shorter than Pennington's was because it was repaired arthroscopically versus cutting.

Pennington also understands that this is Newton's livelihood and the surgery will impact how he approaches football and training for the rest of his career.

"It becomes part of your normal regiment and you're constantly doing things to keep you strong," he said.

Pennington also suggests Newton not get frustrated with inconsistencies, particularly during the first year.

Despite being named the NFL Comeback Player of the Year in 2006, after undergoing a second cuff surgery less than nine months after the first, Pennington said he didn't feel 100 percent in terms of comfort and arm strength until at least a year later.

"I was surviving on my mental capability," he said.

Pennington's first rotator cuff surgery took place on February 4, 2005 while he was playing for the Jets. He returned and started the season before suffering a second cuff injury in the third game against Jacksonville.

He had surgery on October 6.

"I wasn't a 100 percent," Pennington said of the shoulder from the first surgery. "But the injury was not related to me not being 100 percent. The second time around was so freak that it never should have happened."

Pennington started 16 games in 2006, completing 64.5 percent of his passes, close to the 65.4 percent he recorded in 2004. He also threw a career-high 16 interceptions to only 17 touchdowns.

He statistically had his best season in 2008, his first with Miami. He started 16 games, completing 67.4 percent of his passes for a career-best 3,653 yards. He threw 19 touchdowns to only seven interceptions.

"I felt like by '07 and '08 I started to tap back into what I was as a passer and the type of throws I could make on a consistent basis," Pennington said. "When you're rehabbing that shoulder you may make one throw and you feel like you're back to normal, and then the next throw you don't even feel like that was your arm.

"So it's all about staying true to the course and true to the preparation and work load and not get frustrated with the small inconsistencies a surgery like that may create."

Pennington added that setting expectations too high is a sure way for Newton to set himself up for failure.

"That doesn't mean you can't play," Pennington said. "That doesn't mean you can't perform well. You're talking about your central nervous system being disrupted ... your form and flexibility and range of motion being disrupted.

"It takes a while to naturally let those things come back into play."

Pennington began paying more attention to his throwing motion after his second cuff surgery. He said that ultimately made him a better passer.

He would recommend the same for Newton, often criticized for throwing off his back foot and using his arm too much to generate velocity.

"Those two shoulder surgeries made me develop ways to carry more velocity from my body and use my core muscles to generate more velocity," Pennington said. "I wasn't just depending on my arm all the time like I was."

Pennington likes that the Panthers are evolving the offense so Newton, who has more rushing yards than any quarterback in the NFL since 2011, is less involved in the running game. He believes that needed to happen regardless of the injury.

"We get enthralled with quarterbacks that can do things with their legs, but I think this league constantly reminds us that quarterbacks can't survive long periods of time by constantly doing that," he said. "You have to be very judicious in picking and choosing your time."

Newton also has to learn to get down faster and slide better and avoid some of those awkward forward dives that could result in re-injuring the shoulder.

"What you learn is the few extra yards you get as a quarterback, what is the risk-reward for that versus you not being available for your team," Pennington said.

"The biggest challenge is going to be mental, just staying confident in his ability, trusting his program and his training methods and really putting his focus on the mental work."