Thompson was added to the Cardinals' summer camp roster Tuesday, Anne Rogers of MLB.com reports.
The 2019 first-round pick covered 13.1 innings and had 19 strikeouts for High-A Palm Beach last year, and he was likely to end up at Double-A Springfield at some point in 2020 prior to the cancellation of the minor-league season. Thompson is one of the organization's top prospects and is unlikely to see major-league action this year, but his presence at Busch Stadium should aid in his development.