But the striker was back in the PSG side at Stade Louis II on Sunday, scoring a trio of close-range finishes as Thomas Tuchel's men extended their perfect league record to 13 wins.
Neymar added a fourth from the penalty spot and PSG's lead atop the table already stands at 13 points while Monaco are in the mire, with Henry's side only off the bottom on goal difference.
An extraordinary opening 11 minutes saw Cavani score twice with both goals initially ruled out for offside, only to then be awarded after VAR was consulted.
Neymar's cross-shot was turned in at the back post by Cavani for the opener and the Uruguay striker was soon enjoying more delayed celebrations thanks to the video replay system.
Moussa Diaby beat goalkeeper Diego Benaglio to a long Neymar pass, with Cavani on hand to slot into the gaping net.
VAR was needed again before the break when Julian Draxler swapped passes with Christopher Nkunku before beating Benaglio, this time the referral system disallowing the goal for offside.
Cavani grabbed his hat-trick in the 53rd minute, tapping in a Diaby cross to take his tally to eight Ligue 1 goals this season after Adrien Rabiot's throughball had split the Monaco defence.
Djibril Sidibe then brought down former Monaco team-mate Kylian Mbappe in the box, allowing Neymar to roll home a penalty to add his name to the scoresheet.
Mbappe saw a late fifth ruled out for offside after yet another VAR review but the scoreline already reflected PSG's total dominance in a complete mismatch.
What does it mean? Henry powerless amid growing injury crisis
Henry lost both Nacer Chadli and his replacement Jordi Mboula to injury, adding to an already long list of absentees. Senior players including Kamil Glik, Danijel Subasic and Stevan Jovetic were already sidelined, leaving Henry to rely on inexperienced players - far from ideal in what is now a relegation battle. It is hard to imagine more difficult circumstances for his first job.
VAR proves worth with offside calls
The officials had a difficult time with a series of marginal offside decisions in the first half, with VAR helping to clear matters up. Cavani twice saw goals wrongly ruled out on the field and the system was also used to disallow efforts from Draxler and Mbappe. VAR may not be perfect, but it got everything right.
Sidibe struggles amid PSG onslaught
Monaco's injury problems are so widespread it was quite literally men against boys by the end, but Henry would have expected better from Sidibe, one of his key players. The World Cup winner was regularly caught out of position and capped a miserable individual performance by conceding a penalty by bundling Mbappe over.
Key Opta Facts
- PSG have won their last eight games against Monaco in all competitions, their best ever run against them.
- Monaco have won none of their last 12 games in Ligue 1 (D4 L8), their worst run in the top flight since August 1986 (13) and the worst current run in the competition.
- 13 of the 14 teams who registered seven points or less after 13 games in Ligue 1 in the 21st century have been relegated at the end of the season, the only exception being Ajaccio in 2011-12 (16th).
- Edinson Cavani is the first PSG player to score at least three goals in a game against Monaco in Ligue 1 since Carlos Bianchi on May 25, 1979.