Yu Darvish may be the difference between the Cubs finishing first and third in the National League Central. So do you think his spring throwing sessions might be carefully watched? The Dodgers have a similar interest in their shortstop, Corey Seager. If his right elbow is sound, he might be one of the NL's top five players.
And there's Astros second baseman José Altuve -- the 2017 American League Most Valuable Player -- who has already made his pick for 2019 MVP.
"Carlos Correa," he said during the playoffs last fall. That is, if Correa's back is good to go, there may not be a better American League player this side of Mike Trout.
This is where spring drama begins. Amid the comings and goings, some of the most important storylines concern players attempting to bounce back from injuries. Let's take a look at nine who could dramatically impact postseason berths:
1. Yu Darvish, Cubs RHP
Darvish made just eight starts in his first season with the Cubbies before being shut down and undergoing surgery to remove debris from his right elbow. He appears to be completely healthy, and with the addition of Cole Hamels at the Trade Deadline last summer, the Cubs could be the team with the best chance of keeping the Dodgers from winning a third straight NL pennant.

2. Corey Seager, Dodgers SS
He appears to be fully recovered from the Tommy John surgery that limited him to 26 games last season, but the day-to-day grind of Spring Training will be the final test. Dodgers manager Dave Roberts is hopeful Seager will be in his Opening Day lineup. Seager is more cautious, saying he wants to get through a full spring and fully test the elbow before making any pronouncements.
3. Buster Posey, Giants C
The Giants cornerstone has had a smooth recovery from last August's hip surgery, and while team officials believe he could be limited during Spring Training, they are optimistic he'll be in manager Bruce Bochy's lineup on Opening Day. But they'll watch him closely during Spring Training and are committed to monitoring his workload during the regular season. A healthy Posey would go a long way toward getting the Giants back into the postseason picture.

4-5. Jose Altuve and Carlos Correa, Astros 2B and SS
That the Astros won 103 regular-season games with two of their most important players limited by knee (Altuve) and back (Correa) injuries says plenty about the franchise's depth. Correa says he's completely healthy. Altuve, who underwent knee surgery, says he's on schedule, but will be cautious in terms of working his way back for Opening Day.

6. Dustin Pedroia, Red Sox 2B
The Red Sox simply do not know what to expect after Pedroia's left knee issue limited him to three games last season. President of baseball operations Dave Dombrowksi said Pedroia has passed every team and will arrive at Spring Training with the expectation of being ready to go Opening Day. But there's plenty of uncertainty.
7. Jimmy Nelson, Brewers RHP
He says he'll be 100 percent by the start of Spring Training, and if that's true, Nelson may end up being the Brewers' most important addition after not throwing a pitch in 2018 while recovering from right shoulder surgery. He's still only 29 years old and had established himself as the Milwaukee ace before he was injured late in the 2017 season.

8. Albert Pujols, Angels 1B
He appears to have made a nice recovery from last August's left knee surgery. He'll be watched closely in Spring Training and not just because he's 39 years old and approaching his 2,700th Major League game. Once Shohei Ohtani returns, he'll be the Angels full-time designated hitter, which will force Pujols back to first base, where he has started just 98 games the last two seasons.
9. Alex Reyes, Cardinals RHP
Remember when he was the top pitching prospect in the game? Seems like forever ago, doesn't it? Now after two lost seasons and two surgeries, the 24-year-old is throwing free and easy and ready to begin the next chapter of his career. This will be a transitional season in terms of rebuilding his arm strength, but the Cardinals are hoping for a major contribution. Whether that's at the back of a very good bullpen or as a starting pitcher remains to be seen. All that matters is that he has a healthy season. His talent should take care of everything else.