Hartnell was skating when his right leg crashed into Cheechoo's right knee as Cheechoo skated across the ice in the second period of the playoff series opener. Cheechoo's knee bent at an awkward angle and he slumped to the ice nine minutes into the second period.
Cheechoo, who led the NHL with 56 goals last season, stayed down for a few minutes before being helped off by teammates Joe Thornton and Craig Rivet without putting weight on his injured leg.
Hartnell was given a major penalty for kneeing and left with his second game misconduct in three contests.
The Sharks said Cheechoo was being evaluated, and his return to the best-of-seven series opener was uncertain. Cheechoo led San Jose with 37 goals this season, and came in with 20 points in 13 games.