Sanford was injured Friday while battling for the puck in the corner during his group's practice session.
"About three minutes before it happened, I leaned over to one of the coaches and said 'boy, Sandy really is looking good,'" Yeo said. "(I'm) disappointed to see him go into the boards like that, but you always anticipate there will be injuries in training camp and early in the season. We've talked and bragged about the depth we have, so we're still in a good spot here."
Sanford joined the Blues last season as part of the trade that sent Kevin Shattenkirk to the Washington Capitals. The Blues also acquired a first-round pick in 2017, conditional draft picks and prospect Brad Malone in the deal.
In 13 regular-season games with the Blues last season, Sanford scored two goals and three assists. He also made four appearances in the Stanley Cup Playoffs.
