FOXBOROUGH, Mass. -- When Malcolm Butler was transitioning from unheralded Super Bowl XLIX hero to the New England Patriots' No. 1 cornerback at the start of the 2015 season, the coaching staff showed its overwhelming confidence in him in the first game plan of the season by assigning him the task of covering Pittsburgh Steelers receiver Antonio Brown.

That sparked a rivalry of respect between the two, which was followed by their facing off twice in 2016. During that season, as Butler’s star rose, the two also filmed a commercial together for Visa Checkout and Papa John’s.

They meet again Sunday at Heinz Field (CBS, 4:25 p.m. ET).

A player who has been consistently praised in recent seasons by many in the Patriots organization for his competitiveness and for never backing down from a challenge, Butler has always embraced these types of matchups. From a big-picture standpoint, how he fares against Brown and the Steelers (11-2) on Sunday could determine how rich he strikes it as an unrestricted free agent after the season.

Not that he’s allowing himself to think along those lines -- at least not publicly. Butler did everything in his power to deflect any suggestion that his projected matchup with Brown (99 catches, 1,509 yards, nine touchdowns) is a major storyline this week.

“Great player, [but] we have to play well as a team. It’s not just Antonio we have to worry about,” Butler said after the team’s walk-through practice Wednesday.

Asked how Brown challenges him, Butler said, “He challenges everyone. Everybody will have the opportunity to be on him, not just me. You just have to play good football.”

As for what makes the 5-foot-10, 181-pound Brown so effective, Butler said, “Everything. Speed. Heart. Strength. Quickness. All of that.”

“Everything” could also be the best word to describe what Butler’s season has been filled with in 2017, as it has truly been a mixed bag.

After offseason rumors that he could be traded to the Saints, Butler signed his restricted free-agent tender and has been his typical, durable self, playing 97.3 percent of the defensive snaps. He played 96.7 percent in 2016 and 98.8 in 2015.

But unlike in those two seasons, the 5-foot-11, 190-pound Butler has had more inconsistent moments on the field in 2017, with the most recent coming in Monday night’s loss to the Dolphins, when he was in coverage on a Jakeem Grant touchdown catch and then saw Grant get behind him for what could have been another big scoring play later in the game, only to have Grant drop the ball to bail him out.

That was one example of some of Butler’s struggles, which at one point in Week 2 led to his briefly taking on a reduced role and making no excuses for his performance (he quickly returned to front-line role when injuries hit the team’s cornerback corps).

But for every play like that, Butler has delivered at other times, such as alertly punching the ball free from Jets tight end Austin Seferian-Jenkins at the goal line, which was the key play in an Oct. 15 victory. Also, when top free-agent signing Stephon Gilmore missed three games with a concussion and No. 3 corner Eric Rowe was sidelined seven consecutive games with a groin injury, Butler’s presence was vital to the Patriots (10-3). This season, he has two interceptions and a team-high 11 passes defensed.

Asked Wednesday how pleased he is with his level of play, he said, “Umm, it’s all right. It could be better. But it’s not about me. It’s about us.”

It was the type of answer coach Bill Belichick would probably like to hear.

A big challenge awaits Sunday, and if history is any indicator, Butler will be a big part of the Patriots’ plans to cover Brown (23 catches, 316 yards, 1 TD vs. Patriots in last three games).

Butler has loved these matchups in the past, and as free agency looms for this one, it could play a significant role in shaping his future.