On Corey Hart's Rotoworld page, this was the update from February 21:
This was the next update, from March 4:
Corey Hart was sent for an MRI due to swelling in his right knee.
Results of that MRI? Hart was shown to have a torn meniscus. A torn meniscus needs to be repaired with surgery. Can we assert with certainty that Hart wound up with a torn meniscus because the Brewers were having him work out at first base? We can't not assert that.
Hart is having arthroscopic surgery on Tuesday, and it's expected to knock him out for 3-4 weeks. Which isn't that bad, as knee surgeries go. But what this is going to do - probably - is sideline Hart into the season. Not necessarily long into the season, but it's doubtful that Corey Hart will be listed in the Brewers' opening day lineup. That's potentially good news for Norichika Aoki, if Norichika Aoki is a complete jerk who likes when his teammates get injured.
A year ago, Hart injured his oblique in February and didn't debut with the Brewers until April 26, so he's kind of been here before. And he wound up posting an .866 OPS with 26 home runs, so Hart's demonstrated that missing opening day doesn't sink him into a deep, unproductive depression.