There are a number of elite clubs that are on upset alert in the last 16 of the Champions League, and at this stage of the competition, no opponent can be taken lightly.
Every club that has made the knockout stage is capable of pulling off an upset. And as we have seen over the last few years, even title favorites such as Barcelona are not invincible, even on their home pitch.
Let's look at three teams on upset alert in the Champions League Round of 16.
Even though this is a mismatch on paper, Celtic have a good history versus Juventus and will not be intimidated by the talent and skill that the Serie A club brings to the pitch.
Celtic played very well against Barcelona in the group stages, which should give them plenty of confidence in the knockout stages. They nearly drew at the Nou Camp and pulled off an amazing upset when the Spanish club traveled to Celtic Park.
Both clubs are strong defensively, and it's hard to imagine either team scoring many goals in this fixture.
Celtic proved in the group stage that they are not afraid of the top-tier clubs and never give up regardless of the challenge. If Juventus do not win at Celtic Park in the first leg, an upset will be possible.
French side Paris Saint-Germain have one of the most talented rosters among the clubs still alive in the Champions League, but their matchup versus Valencia will not be a walk in the park.
Despite the impressive amount of attacking talent that each team displays on the pitch, the strength of these clubs is their defense.
PSG and Valencia were among the eight clubs in the group stages that allowed fewer than six goals in the six matches. Therefore, even though each club's most talented players are goal scorers, defense and goalkeeping will likely decide the outcome of this fixture.
Valencia are certainly capable of continuing their strong defensive play and frustrating the PSG attack. It won't be easy, but upsetting the French side is not an impossible task for Valencia.
Borussia Dortmund avoided a matchup with one of the title contenders in the Round of 16, but Shakhtar Donetsk proved in the group stage that they are capable of beating anyone. Just ask Chelsea and Juventus—two clubs that found Shakhtar difficult to play against in the group stages.
The last time Shakhtar played in the knockout stages of the Champions League, they defeated Serie A side Roma 6-2 on aggregate during the Round of 16 in 2010-11.
If there's one club that can make a surprise run to the semifinal, it's Shakhtar Donetsk. Dortmund must defend properly, because playing a high-scoring type of game against Shakhtar is not a winning strategy.