Every year when we get to Memorial Day, MLB teams evaluate where they stand and come away with a pretty good idea of what they need to do between that point and the trade deadline, which this year is Aug. 3. One of the more difficult aspects of the evaluation is when veteran players are performing well below their accustomed level. That’s when teams have to figure out if the underperformance is just an early-season slump or due to injury, mechanical issues or the harsh reality that the player is another year older and perhaps their decline in performance is here to stay.Predicting when a veteran player is in permanent decline is difficult because some players, like David Ortiz or Adrian Beltré, can continue to perform at a high level into their 40s. Some players start their decline in their early 30s, like Carl Crawford or Hall of Famer Andruw Jones.Bottom line, how a player will age is not something that’s predictable. When a player loses some hand-eye coordination and bat speed, it doesn’t come back. During the performance enhancing drug era, players were able to perform well into their late 30s at a high rate, but those days are now behind us.There is a recent group of Hall of Fame caliber players who declined earlier than expected, including Miguel Cabrera, who after hitting over .300 with more than 30 homers almost every year, declined immediately after age 33. He still played seven more seasons but never hit 20 home runs or .300 again.Joey Votto led the National League in on-base percentage seven times, and through age 33, he averaged nearly 30 home runs per season. After his age-34 season, where he led the NL in OBP, he declined as a hitter, never reaching base at a .400 clip again and hitting more than 15 home runs just one time over his final five seasons.Star veteran players who begin their decline phase can still be useful major leaguers but expectations about what they can contribute have to be adjusted.This season, we’ve already seen several star veteran players get off to extremely slow starts. Their teams must now decide if these players can bounce back or if their stars are in a decline phase that is permanent. I took a look at some of those underperforming star players and made my best assessment as to whether these players are just in a slump or on the downslope of their careers.(Note: Stats as of Tues., May 19.)Manny Machado, 3B, San Diego PadresMy best guess: He’ll reboundMachado, 33, has been one of the best third basemen in the league since he arrived as a teenager in 2012. Since 2019, he’s also been the face of the Padres’ organization. He’s been extremely consistent at the plate, hitting at least 32 home runs a season from 2015-19 and at least 27 home runs in every season since 2015, save for the shortened pandemic year. He’s also driven in at least 85 runs in each of those seasons.This year, he’s off to the worst start of his career, slashing an ugly .182/.277/.339 with an OPS+ of 73. According to Statcast, his bat speed has declined from 74.5 mph to 74.1 mph from last year to this season. It was 76.7 mph in 2023, the first year for tracking that metric publicly. His bat speed is still above-average for the league, but his attack angle has dropped from 8 degrees last season to 6 degrees this year (the ideal attack angle for hitting line drives and home runs is between 5 and 20 degrees) and he’s hitting the ball more to the opposite field than he has in any of the past four seasons.Perhaps a change in mechanics or approach can get that attack angle back up at least to last year’s levels and get him to hit the ball more up the middle or to the pull-side again.Ortiz’s age-33 season was in 2009, and he got off to a slow start, hitting just .230 that April and an ugly .143 that May. He looked like he was declining. He then hit .320 in June and went on to perform at a high level through age 40. Hopefully, that’s going to be the case with Machado, considering he’s signed through 2033 (when he will be 40) at over $39 million per year.