As I write this, 21 undefeated teams remain at the FBS level. Of those 21 teams, 16 are Power Five teams. Most of these teams will not finish the regular season undefeated. Hell, based on recent history, odds are none of them will.

We haven't seen a Power Five team finish a season without a loss since Florida State did it in 2013. What we have seen plenty of is teams getting off to 3-0 or 4-0 starts to seasons only to fade as conference play begins. That's an annual rite of passage as teams take advantage of weak nonconference schedules to boost their record as much as possible and try to stave off reality for as long as possible.

Reality always comes, however, and it's the motivation for this week's Friday Five. I've gone over the 16 undefeated Power Five teams in search of the five most likely to finish the season with at least four losses. This isn't a prediction that they will as much as it's a look at the probability of it occurring for each team based on how they've played to this point.

5. Duke

There are some extenuating circumstances here, the biggest of which is that Duke quarterback Daniel Jones is dealing with a broken collarbone. He will return this season and could return in the next couple of weeks. The good news for Duke is that it has managed to go 2-0 without Jones, beating Baylor and North Carolina Central. But, even with Jones, the chance for a four-loss season exists.

The Blue Devils have games remaining against Virginia Tech, Miami, Clemson, and a Virginia team that looks to be formidable to this point. While Georgia Tech and Pitt haven't been impressive, the Blue Devils will play both on the road, and then there are games against North Carolina and Wake Forest. Both of those are at home, but they're also state rivals, and things can get weird in rivalry games.

4. NC State

Sticking with ACC schools in North Carolina, we have NC State. The Wolfpack is 3-0 with wins over James Madison, Georgia State and Marshall. Some might tell you the most impressive win of those three is the one against James Madison. Others might say to you that, had the game not been canceled due to Hurricane Florence, NC State would already have a loss to West Virginia. I'm not sure either statement is true, but they're both defensible.

Either way, the Pack has games remaining against Virginia, Boston College, Clemson and Florida State. Clemson is the only one of those four on the road. That doesn't mean the road schedule doesn't include some potential pitfalls, though, as Syracuse is tough at home and finishing the season with back-to-back road games against Louisville and North Carolina might not be as easy as it looks right now.

3. California

Cal is 3-0 and currently ranked No. 24 in the AP Top 25 poll, but Cal has also only scored 90 points in three games, with half of them coming last week against Idaho State. It's a team built around a defensive identity, and while there isn't anything wrong with that, teams that struggle to score points struggle to win consistently in this era of college football.

I mean, even Alabama eventually realized it needed to start scoring points.

And that's where my concerns about Cal going forward lie. The Pac-12 looks weak to this point, and maybe Cal could take advantage, but it also resides in the one Pac-12 division where a lot of the conference's strength lives. Things will start this week against Oregon, but the Bears also have to play Washington and Stanford later this season, and there's a road trip to USC in November as well.

2. Syracuse

I just told you that I worry about Cal because it struggles to score points, but that is not Syracuse's problem. It will score. The question I have is whether or not Syracuse can stop anybody from scoring. Now, I have to mention that the Orange have only allowed 38 points in the last three games after giving up 42 to Western Michigan in the opener. The problem is that the last three games came against Wagner, Florida State and UConn.

Holding Florida State to one touchdown is, and always will be, a good thing. I don't know if I'm confident that it was a reflection of Syracuse's performance or Florida State's at this point. And allowing 21 points to a UConn team that scored nearly 56 percent of its points this season in one game against Rhode Island doesn't bode well.

Furthermore, Cuse plays on the road at Clemson this weekend and has games left against NC State, Notre Dame and Boston College. Those are the most likely losses, and there are also potential pitfalls on the road against Pitt and Wake Forest.

1. Colorado

The Buffaloes are off to a 3-0 start to the season, and everybody is feeling good. I'm just not sure how good they should be feeling. Yes, the Buffs are 3-0, but they're 3-0 with wins over Colorado State, Nebraska and New Hampshire. Those three are a combined 1-10 on the season. Advanced metrics aren't a big fan of Colorado to this point, as the F/+ ratings from Football Outsiders have this team ranked No. 67 in the country. For perspective, Florida State is at No. 57.

Also, let's not forget that Colorado began the 2017 season with a 3-0 mark as well, beating Colorado State, Texas State and Northern Colorado. What followed was seven losses in Pac-12 play.

I don't believe the same fate awaits for these Buffs. From what I've seen, this looks like a bowl team. Still, even so, with games remaining against Arizona State, USC, Washington, Washington State, Utah and Cal, it's hard to envision Colorado getting through the year without at least four losses. Though, as somebody who has always been partial to watching Ralphie run onto Folsom Field, I'm hoping it doesn't happen.