"Don't it always seem to go that you don't know what you've got 'till it's gone.”

That well-known lyric from Joni Mitchell’s 1970 song “Big Yellow Taxi” fits perfectly with the gut-wrenching feeling that accompanied the news of Cale Garrett’s injury, which Missouri football announced late Sunday night.

The Missouri co-captain and defensive standout at linebacker has a pectoral tendon ailment and is having surgery to repair it — most likely ending his breathtaking, shortened senior season.

Calling it a tough break for Garrett may be the ultimate understatement.

His Missouri career likely won’t end on his terms. Instead, the final moment may have been hearing the diagnosis from a doctor over the last 48 hours, spoiling his two-interception performance during a 42-10 drubbing of Troy and his third defensive touchdown in as many games.

While having surgery and taking a break from football is necessary for his long-term health, this is a gut-punch.

Garrett was a well-respected, extremely-trusted voice and presence for the Tigers' defense, which currently ranks second in the nation in yards allowed per game.

“His instinctual feeling of how to go play is off the charts,” Missouri head coach Barry Odom said of Garrett after Saturday's victory against Troy. “He’s the heart and soul of our team.”

Odom has long known how integral Garrett is to his team. But now it appears his value is priceless.

His injury occurred in the fifth game of the season — one more than the NCAA allows to retain a standard redshirt. A medical redshirt may be possible, but it’s unclear whether that’s something Missouri would pursue or Garrett has any interest in.

The media on the Missouri football beat spent a few months stating how vital Tigers quarterback Kelly Bryant was for Missouri to be successful. Local outlets, including the Tribune, lauded his potential of being unleashed in Derek Dooley’s offense.

We’ve seen evidence of that through five games, as Bryant has been proficient with his arm and legs. His 2019 journey is expected to continue after suffering a left knee sprain and also exiting the game in the win over Troy.

Neither Bryant nor Garrett were available to speak with reporters after the Tigers’ blowout victory Saturday.

The reason for Bryant’s absence from the postgame media session was obvious. His injury received lots of attention. Odom and his players responded to questions about Bryant by citing their next-man-up mentality with backup QB Taylor Powell.

The fact Garrett wasn’t in attendance flew under the radar. A team spokesperson said Garrett was “getting treatment” — that could mean almost anything — but provided no further detail.

Garrett's injury was a well-kept secret Saturday night, even as praised poured in on the national level.

“It's time to start thinking about Missouri's Cale Garrett as an All-American," CBS Sports' Dennis Dodd tweet late Saturday.

With Bryant likely suiting up against Ole Miss on Saturday, and Garrett potentially having already suited up for the last time, now it's safe to wonder whether Missouri’s “quarterback” on defense that was the most important Tiger all along.

That’s not to say Jamal Brooks nor Cameron Wilkins, the likely replacements for Garrett, can’t do an adequate job.

Nick Bolton, who has started alongside Garrett at linebacker all season, is in the middle of a breakout campaign with 36 tackles, three tackles for loss, two interceptions and a defensive touchdown against West Virginia.

However, Garrett’s impact is nearly immeasurable.

After a career-high, 16-tackle performance against Wyoming, he was one of the first to say there was no excuse for the season-opening loss.

Garrett backed up his words with seven tackles and a sack during a win over West Virginia the next week.

Then he played the role of hero against Southeast Missouri, South Carolina and Troy. Garett found the end zone in each game. He’s actually tied for fourth on Missouri in scoring.

Tucker McCann is first with 45 points. Albert Okwuegbunam and Larry Rountree are tied for second with five touchdowns apiece. Then there’s Garrett, Tyler Badie and Jonathan Nance, each with three touchdowns.

“It’s special, one of a kind,” Bolton said Saturday of Garrett’s defensive dominance, before news broke about his injury. “It doesn’t really happen that often and so it’s special being around somebody who loves playing the game, loves his community, this is his university, he’s from Kansas City. This is what he lives for.”

It’s unclear exactly when the Kearney High School graduate sustained the fateful injury. There are videos circulating on social media of two possible occurrences.

One is on the last play of the first quarter, when Troy wide receiver Kaylon Geiger hit Garrett above the waist as the play ended with the Tigers linebacker noticeably grimacing.

The other is when Garrett was tackled chest-down on his first interception return, as three Trojans, with a combined weight of approximately 800 pounds, brought him to the turf. A sideline video shortly after the play shows Garrett in some discomfort.

Garrett will have immediate surgery to repair his pectoral tendon.

The next time we see Garrett playing football could be the NFL Combine in February.

Through five games, Garrett’s ability jumps off the screen. But it’s still only five games, and there will be a lot to prove to professional scouts should he decide to pursue an NFL career.

Garrett has a team-high 43 tackles, five tackles for loss, two sacks, three interceptions and three defensive touchdowns.

The Tigers now turn to other defensive playmakers, including Bolton, lineman Jordan Elliott and cornerback DeMarkus Acy.

The defense may no longer be as elite as it was with Garrett, but the strong nucleus he helped foster remains in place. Even with the loss of Garrett, not all is lost. The likes of Ole Miss, Vanderbilt and Kentucky will have to stop Bryant and the Missouri offense the past three weeks.

Time will only tell how this unit responds to the loss of its leader, who as of Monday is off the Tigers' active roster.

Just like that Mitchell lyric suggests, Missouri had one of the best linebackers in America near the midpoint of the 2019 college football season.

Now, the question is this: Who will fill the void he leaves behind?