This is must-see Instagram.

Former 49ers safety Donte Whitner spent Monday afternoon posting critical Instagram video clips of current 49ers cornerback Ahkello Witherspoon. Whitner even used a telestrator and slow motion just to show just how worthless Witherspoon is at his profession.

The 49ers drafted Witherspoon in the third round last year.

To view Whitner’s video, click here, then click on Whitner’s picture at the top-left corner of the page. The video clips should start immediately.

If you can’t view the clips, here are the highlights.

Note: Sometimes Whitner talks about Witherspoon, and other times Whitner addresses him directly.

WHITNER: “Watch how this receiver doesn’t respect you (speaking directly to Witherspoon). That starts something you don’t want. Receivers are attacking you after the play. That may seem like a small thing, but it’s attitude. Are you going to push him back? What are you going to do? Get pushed around all season?”

WHITNER: “You’re supposed to be here and you’re lollygagging. There’s no sense of urgency to get back and do it properly.”

WHITNER: “Even when (Witherspoon) does get a press sometimes, he’s still not doing any damage because he’s not stronger than the wide receiver. He needs to work on his upper-body strength.”

WHITNER: “(Witherspoon) shows he has all the physical capabilities to get it done. Good back pedal. Good job widening the receiver, looking back for the ball, getting him toward the sideline. He can do it, but can he do it each and every snap? That’s the problem.”

WHITNER: “The tackling is an issue. (Witherspoon) is shooting low and just rolling, not wrapping. Teams see this on film. Run through his facemask. You’re a 6’3″ corner.”

WHITNER: “Preseason game No. 3. This is the dress rehearsal. (Witherspoon) is supposed to be getting ready and tuned up. No jam. Open the gate. This guy is running wide open. These are things that come back to bite you in the season.”

WHITNER: “Man-to-man coverage again. You’re supposed to be getting tuned up for the season. You open the gate, jam with the wrong hand and this guy is open a-gain. Teams watch this film.”

WHITNER: “Here’s that go-low-and-roll type of thing. How many tackles do you think you’re going to miss doing that?”

WHITNER: “Third and five. Man to man. Bad technique from the get go. No jam. Opening up the gate. You’re letting the guy run straight down the football field, so now you have to grab and get a P.I.”

WHITNER: “Things last year were covered up for this guy. When you win at the end of the season, you can give up a couple plays people will overlook. But when you’re losing, they’re going to nitpick everything.”

WHITNER: “No sense of urgency to get over there. And then watch what the receiver does to (Witherspoon). (The receiver shoves him). I told you. It’s all about attitude.”

WHITNER: “I told you about bad eyes on the back side. You have this guy here. Don’t be looking in the backfield. That’s your man running open. These things come back to bite you if you don’t correct these things.”

WHITNER: “Are you really trying to get off this block, or are you just getting ran out of bounds? Like, come on.”

WHITNER: “Now we’re in to Week 2, and now they get film. They’re starting to scheme. You see this wide receiver motion down. Here’s (Witherspoon). Look what they do. They know he has bad eyes. Run play action here, get his eyes here (on the running back) because he’s undisciplined and doesn’t want to watch his guy, and they slip this receiver right behind him. It’s all fundamentals, things that started in the preseason that didn’t get corrected.”

WHITNER: “Here’s a play that shows the willingness to get to the football. We see you covering the guy. The ball goes here (away from Witherspoon). Everybody else is reacting but you. That’s what makes a good defense — everybody, even the backside corner, has to run and react to the football.”

WHITNER: “We talk about want-to. The back is here. (Witherspoon) can get off of this block and make this tackle. Or did he just pull back? I think he just pulled back.”

WHITNER: “Here’s another one. Because of your unwillingness to jam or stay square or be physical, you’re going to get double moves all year long.”

WHITNER: “Here’s the first time (Witherspoon) threw a teammate under the bus.”

WHITNER: “Here we go, Cover 2. (Witherspoon) is (supposed to) jam the man, open up, take away this (sail) route and then come up to make the tackle in the flat. Let’s see what we get. No jam. Break. Dive. Miss. That’s just bad football.”

WHITNER: “You’re really hoping they throw a bad ball. And then you celebrate. You didn’t affect this play at all.”

WHITNER: “Watch this. This is sickening. Look at this effort (Witherspoon is jogging across the field). (The running back) is still running. He’s still running. He’s still running.”

WHITNER: “Now the league has film. (The Cardinals) put one of their fastest guys (on Witherspoon). First play of the game. Let’s see what happens. No jam. Let the guy run. Now we have a 75-yard touchdown.”

WHITNER: “This is (Witherspoon) doing it correctly, and this is what is should look like every time. I was starting to think he couldn’t do it, but here it is. Watch the jam. Physical. On top of the route.”

WHITNER: “Another play showing effort. Somebody must have talked to (Witherspoon). Getting to the football and trying to be physical. Somebody must have said something.”

WHITNER: “Play No. 1, Week 8. Remember how I talk about how receivers don’t respect you and think you’re soft? Well, let’s see how this receiver attacks you first play of the game. Running play. (The receiver shoves Witherspoon in the face). They’re seeing it on film.”

WHITNER: “You get off the block. Good job. Got the (ball carrier) in a phone booth. You close your eyes and launch and miss. No contact courage. Give me some courage out there.”