As the start of baseball season approaches tomorrow, a lot of people are worried if Jose Canseco can come back from his troubles with the police and his divorce, if Rickey Henderson can keep his mind on the game knowing his $3 million is $2 million below high pay, if Barry Bonds can be happy in Pittsburgh at only $3.5 million this year, if Eric Davis can get over not being flown from Oakland to Cincinnati after last fall's World Series.

These are small-time worries, however, when compared to those of Mackey Sasser and Nick Esasky, two ballplayers who are coming into the 1991 season with genuine big-league problems. If you're looking for somebody to pull for who's really got something to overcome, consider these guys. To them right now, a contract dispute would be like facing a batting practice pitcher in the bottom of the 9th.Sasser is a catcher with the New York Mets and Esasky is a first baseman with the Atlanta Braves. Esasky has played seven years in the big leagues, for Cincinnati, Boston and Atlanta, with a lifetime batting average of .251, capped by a .277 average, 30 home runs and 108 RBIs in his last full year of baseball, in 1989 with the Red Sox.

Sasser has played four big-league seasons, with San Francisco, Pittsburgh and the Mets, for whom he hit .307 last year as their most consistent starting catcher.

But last season was not a bright one for these players, and it didn't have anything to do with agents or salary problems or personality clashes with their managers.

Esasky, out of nowhere, was plagued by vertigo, and Sasser, out of nowhere, was plagued by the baseball version of the yips.

A year ago, early in the 1990 season, Esasky, fresh from signing a three-year, $5.7-million contract with Atlanta, noticed something strange about popups he was camping under. He'd see three of them. He didn't know if he should catch the ball on the left, the right, or in the middle.

Everything was blurry. Fastballs coming to the plate at 90 mph were more of a blur than they'd ever been. Hitting the curveball wasn't so much a problem anymore. Finding it was the problem. He couldn't run long distances without falling over. When he got in his Mercedes to drive home, he didn't dare drive over 20 mph. After 35 at-bats, and 14 strikeouts, and five fielding errors, his 1990 season was over.

In the 12 months since, Esasky has been working hard at beating the vertigo. He has seen specialists. He had his teeth fixed. He had his vision checked. He had his ears probed. He consulted with the Dizziness and Balance Center in Wilmette, Ill. They gave him a good news-bad news report. First the good news: His condition was physical, caused by a virus. It was not all in his mind. He wasn't crazy.

The bad news was they didn't know how to cure it.

As for Sasser, his problems began midway through last season, when, on throws back to the pitcher, he started to tap the ball into his glove a time or two. Then it occasionally became four or five taps. Then, sometimes, as he stood up to wrench the ball out of his glove, he'd occasionally lose his balance and have to have the umpire help him stay upright.

He still had his big-league arm for stealing attempts to second or third. Only the little throw-backs to the pitcher - like short putts for golfers - were affected.

Baseball historians pointed out that Sasser wasn't the first catcher to experience this kind of problem. Old-time catchers, including Randy Hundley of the Cubs, Johnny Edwards of the Reds, Sammy White of the Red Sox and Clint Courtney of the old St. Louis Browns, among others, had their flings with the yips. Edwards, supposedly, resorted to going to the front of the plate and tossing the ball back like a girl.

Their problems, as well as Sasser's, were diagnosed as mental.

The Mets hung with Sasser, and his .300-plus average, through last season, but when a couple of teams took advantage of his stuttering by stealing bases late in the season, they got nervous. When the problem wasn't cleared up this spring - the yips only occur in games, never in practice - they got more than nervous.

When the season starts tomorrow, Sasser won't. He'll be the Mets' third-string catcher, hanging on as a pinch-hitter.

At that, he's in better opening-day shape than Esasky, who, despite a good deal of improvement over last year, didn't make the Braves' big-league club, but will be assigned later this month to either a AA or AAA farm team.

The bright spot in both stories is when you listen to Sasser and Esasky themselves.

"There have been a lot of things cured by God or by sheer willpower," said Esasky. `There have been miracles that no one can explain. So that can happen."

"It's getting better," said Sasser. "A lot of guys would quit if they had this problem. I'm not a quitter."

They're down but they're not out. It's conceivable they could be back to their old whole selves before this season is history, that one day this summer Esasky could come to the plate against the Mets, with Sasser catching, and there will be one ball pitched and one ball going back in a smooth motion to the mound.

Such an event wouldn't rate the attention of Henderson signing a new $5 million contract, but it would be some double triumph just the same - of mind over matter, and matter over mind.