The Captain America (Chris Evans) that we'll see in Avengers: Infinity War is a very different man than the one we saw in The First Avenger, The Winter Soldier, and Civil War. For one thing, he's a war criminal (per Hannibal Buress in Spider-Man: Homecoming) wanted by the United States government.
For another, he doesn't have his Vibranium shield. What he does have is longer hair and a scraggly beard, as evidenced by the first Avengers 3 trailer. For all intents and purposes, he's basically just Steve Rogers, which was the very intent of director Joe and Anthony Russo, whose success on making the last two Cap movies landed them the gigs of directing Infinity War and its currently untitled sequel.
Speaking to the Fantasy Focus Football ESPN podcast, Joe said, "Our approach to the character [Captain America] was to deconstruct him, was to take him in a different direction. Obviously you can't deal with a character called Captain America without dealing with the thematics behind that, so we wanted a relevancy to it and we wanted to put him in a position where he was questioning the chain of command. Into these Avenger films, he's on a very specific journey as a character."
With Steve stripped of all the things that make him Cap, some have theorized that he will be assuming the role of Nomad in Avengers 3. Debuting in 1974's Captain America #180, Nomad is the persona that Rogers took up after abandoning the title of Captain America. He makes this difficult decision after learning that a powerful U.S. politician is the leader of the terrorist organization known as the Secret Empire; since this issue came so soon after the Watergate scandal and Nixon's resignation, the politician is hinted to be Tricky Dick himself. However, Hawkeye convinces Cap to remain a hero and Steve agrees, albeit becoming a champion of good with no nation, hence Nomad. This was a short-lived fling (he even tripped over his own cape at one point), and he returned to the position of Captain America after realizing he could uphold American ideals without blindly supporting the government.
So, will Captain America become Nomad in Infinity War? The answer is yes and no, according to Joe Russo.
"I wouldn't say that he is exactly Nomad, but he is the spirit of that character," he said.
You can listen to the full podcast here.