Washington Redskins running back Chris Thompson, right, avoids a tackle by New York Jets strong safety Calvin Pryor on Oct. 18. (Seth Wenig/Associated Press)

Chris Thompson had a teachable moment last month when he suffered a lower-back injury in Week 6 against the New York Jets. It wasn’t a mental mistake, however, but rather an equipment error by the second-year running back.

Thompson landed directly on his lower back while leaping for an overthrown pass attempt from quarterback Kirk Cousins. It was the one portion of his back that wasn’t protected by his back pad. He was injured on the play but later returned and played the rest of the game. Thompson has had a small back pad, ending around his mid-back, since he received his shoulder pads during the summer. Although running back Alfred Morris has repeatedly reminded him to get a longer back pad to protect his lower back as well, Thompson never did.

Right below Alfred Morris’s numbers is a back pad that protects him from injury. (John McDonnell/The Washington Post)

“I just never traded them out. I should have, and Alfred kept telling me I needed to switch, but I just didn’t do it,” Thompson said. “It was a teaching lesson for me.”

There wasn’t any padding on Thompson’s lower back once it slammed against the MetLife Field turf. Thompson has now ordered a longer back pad, which he expects will arrive on Wednesday.

“It’ll help a lot,” Thompson said. “I’ll have a little more cushion back there because I’m going to end up falling on my back at some point.”

The Florida State product has missed just one game so far, the team’s Week 7 victory over the the Tampa Bay Buccaneers, with the back injury. The swelling has resided over the past two weeks, but Thompson still had a baseball-size knot in his back following Monday’s practice.

“It was a lot bigger than that the Monday after [the game],” Thompson said. “You can’t do anything about it. It’s basically just a pack of blood sitting right there. You’ve just got to let your body work it out on its own. You can try to massage it out a little bit but it doesn’t help. Nothing helps but my body naturally. Only time can heal it.”

Thompson was active during the team’s short practice session on Monday, and he’s optimistic about playing on Sunday against the New England Patriots despite the knot. Thompson doesn’t feel any pain in his back at this point.

“I’ve been able to run for maybe two or three days now, so it’s more about being able to play football,” Thompson said. “I know I can run. I know I can sprint, but turning and catching, being able to get in and out of my breaks.”

More from The Post:

Gruden: Redskins need to have their best week of preparation for Pats

Jackson vows to play vs. Pats | Kerrigan and Lichtensteiger practice

Opening Kick: Redskins’ bye week gets sweeter with rivals’ losses

Griffin in awkward spot at NFL trade deadline | Bog: Teammates praise him

More NFL: Redskins | Around the league | Bog on Redskins | Fantasy

Follow: @MikeJonesWaPo | @lizclarketweet | @MasterTes | @Insider