The Eagles, who have faced four quarterbacks this season that were the No. 1 pick in the NFL draft, will go up against a guy Sunday who was the No. 1 quarterback selection in the Alliance of American Football draft.

Two weeks before the Redskins signed Josh Johnson earlier this month, and three weeks before he became the team’s fourth starting quarterback, he was selected by the San Diego Fleet in the AAF’s inaugural draft.

For those who have no earthly idea what the AAF is, it’s an eight-team spring developmental league that will begin play in early February.

The 32-year-old Johnson also was an NFL draft pick – back in 2008. He was selected by the Tampa Bay Bucs that year in the fifth round. Since then, well, he’s been around.

Look up journeyman in the dictionary and there’s probably a picture of Johnson. The deal he signed with the Redskins earlier this month was his 20th contract with 12 teams.

Until he replaced Mark Sanchez in the third quarter of the Redskins’ 40-16 loss to the Giants on Dec. 9, however, he hadn’t thrown a pass in a regular-season game since 2011.

Six weeks ago, things were going swimmingly for the Redskins. They were 6-3 and led the NFC East by two games. Then their starting quarterback, Alex Smith, suffered a gruesome leg injury in a Week 11 loss to Houston.

Two weeks later, in a 28-13 loss to the Eagles, Smith’s replacement, Colt McCoy, broke his leg.

Sanchez, signed off the street just a week earlier, replaced McCoy, and the Redskins added Johnson, presumably to back up Sanchez.

But Sanchez was Sanchez. Turned the ball over too much, wasn’t very accurate and didn’t have the mobility that Johnson possessed. He made just one start before head coach Jay Gruden benched him and handed the ball to Johnson.

“Once Colt went down, we thought it was in our best interest to get a guy with a little more mobility that could escape some of these pass-rushers and use his legs a little bit more,’’ Gruden said.

“I had Josh in Tampa [in 2008] for a little while. And then I brought him to Cincinnati with me. So I knew what type of athlete and guy he was as far as retaining information.’’

The Redskins’ offensive line has been ravaged by injuries this season. They’ve gone through nine guards. The pair they started last week in a 25-16 loss to Tennessee – Luke Bowanko and Zac Kerin – have just five starts between them over the last four seasons.

Johnson is an elusive runner, who is averaging 5.8 yards per carry and has seven of the Redskins’ 17 rushing first downs in the three games he’s played.

In his two starts, the Redskins have run the ball 67 times and thrown it 58. Against Tennessee last week, Adrian Peterson rushed for 119 yards on 26 carries. The 26 carries equaled his season high.

“With the way AP has been playing, they’re obviously committed to [the run,’’ Eagles defensive end Chris Long said. “It’s going to be a challenge.

“You win games in December running the football. That’s what I’m sure their mind-set is going to be. Especially with the injuries at quarterback. But Johnson has done a good job.’’

“They’re playing to [Johnson’s] strengths,’’ defensive tackle Fletcher Cox said. “He’s somebody that can beat us if we let him. We’re got to make sure we do our No. 1 thing, and that’s stopping the run, stopping Adrian Peterson. The last time we played them, he had a 90-yard touchdown run against us.’’

Before signing with the Redskins, Johnson had made just five NFL starts and with five touchdown passes and 10 interceptions in 177 career attempts.

In his two starts with the Redskins, he has a 75.3 passer rating, including two touchdown passes, two interceptions and a 6.3 yards-per-attempt average.

But his ability to elude a rush is going to present the same kind of challenges for the Eagles as the myriad of other mobile quarterbacks they’ve faced this season.

“He’s a good player,’’ Long said. “We have to be responsible with our rush lanes. I think he’s a good thrower, though, too. We can’t just think of him as a running quarterback.’’

Said Eagles defensive coordinator Jim Schwartz: “He’s made a lot of big plays the last couple of weeks. His ability to keep plays alive with his feet is similar to what we’ve seen from a lot of guys this year. From people like [the Panthers’] Cam Newton, from [the Texans’] Deshaun Watson.

“But that’s not the only thing. He’s made some really nice throws. You can see the fact that he’s been around the NFL for a long time. He’s very composed. Knows how to run their offense. Even though he hasn’t played a lot, there was a reason he kept catching on with another team. It’s because he’s talented, and we’re going to have our work cut out for us.’’