Fleury (undisclosed) will be available to return to the lineup in Game 5 against Florida on Monday, according to Gabby Shirley of Bally Sports Florida.
Hagel scored two goals, one shorthanded and the other the game-winner, and added a power-play assist Saturday in a 6-3 victory over the Panthers in Game 4.
Stamkos deposited two goals, including a power-play tally, in Saturday's 6-3 win over the Panthers to stave off elimination in Game 4 of the conference quarterfinals.
Sergachev (leg) was activated off long-term injured reserve, per the NHL media site, which sets him up to return for Game 4 against Florida on Saturday.
Stamkos scored a goal on two shots and added six hits, two blocked shots and a minus-2 rating Thursday in a 5-3 loss to the Panthers in Game 3 of the Lightning's first-round series.