Red Guardian said he fought Captain America in the 1980s, so it's obvious he meant Steve, but even then, the story is apparently a fabricated version told by Alexei due to Steve still being on ice until 2011. This was likely to further boost up Alexei's rep among the inmates. Being during the events of Black Widow, which took place in 2016, at least 7-8 years before Steve gave Sam Wilson the shield and eventually Sam took up the title.

I'm telling you, it's has be Old Man Steve unless Alexei miss the fact that "Cap" was either Black or has a metal Arm lol. It's the only thing that make sense to me because I don't think that he lying about it to the inmates because why would he mention it to Nat during the run?

For one, they were separated when they were on the run.

Another thing is he would lie even if it wasn't Steve to make the story greater. In his opponent being the great Captain America his country always compared him to.

Soviet propaganda. Red Guardian never fought any Captain America.

...imo

While the time it probably have been Steve

The only other guess would be Isaiah Bradley

@Masteruniverse 95

It could be William Burnside?

Who isn’t in the MCU yet.

It could be offscreen, maybe they might do that!?

Maybe due to Steve traveling in time during Endgame?

William Burnside would make sense.