Chiarelli said McDavid, the first overall pick in this year's draft, will require surgery after breaking his collarbone in Tuesday night's 4-2 win over the Philadelphia Flyers.
McDavid got tangled up with Philadelphia defensemen Michael Del Zotto and Brandon Manning, who also lost their balance on the play, and fell shoulder-first into the end boards behind the Flyers' net.
The 18-year-old McDavid was slow to get up after the collision and was holding the shoulder with his gloved hand as he skated to the bench. He was later seen with his left arm in a sling.
"I just saw him and told him to keep his head up," coach Todd McLellan said after Tuesday's game. "He's disappointed he got injured. It's his rookie year, and it's going really well, and he wants to be part of the group ... which he still will be. He's just not going to wear the uniform for a while."
Hall of Famer Wayne Gretzky was watching when the injury occurred.
"I knew as soon as he went into the boards," Gretzky told ESPN's Pierre LeBrun on Wednesday. "They're so fast and big now in today's NHL. It's incredible how fast the game is. From the positive side, I'm just glad the two Flyers players did nothing illegal on the play. It was a hockey play gone bad."
McDavid leads NHL rookies with five goals and has seven assists in 13 games for the Oilers. He was second in scoring for the team and was named the league's Rookie of the Month for October.
Information from ESPN's Craig Custance, Pierre LeBrun and The Associated Press was used in this report.
Melrose: 'A dark day for Edmonton'
Barry Melrose discusses the unfortunate injury to Oilers phenom Connor McDavid and the injury history of Edmonton's recent top draft picks.
McDavid leaves after sliding into boards
Oilers rookie Connor McDavid leaves Tuesday's game against the Flyers with an apparent shoulder injury after sliding into the boards. Edmonton wins the game 4-2.