|Bayer Leverkusen's Mexican forward Javier Hernandez (known as 'Chicharito') celebrates after scoring during a German first division Bundesliga match against FSV Mainz 05 in Mainz, western Germany, on September 24, 2016|
The 28-year-old netted a hat-trick -- his second in Germany's top flight -- in helping Leverkusen come from 2-1 down to claim a 3-2 win at Mainz on Saturday.
"Thank God, he's in form at just the right time," said Leverkusen's coach Roger Schmidt after the Mainz fightback.
After five years at Old Trafford, Chicharito quit the Red Devils in August 2015 for Leverkusen's 'Werkself' and has banged in 21 goals in 32 league games in Germany's top flight.
Having fractured his arm in an accident at home in August, Hernandez was not fully fit when he played the first 45 minutes of Leverkusen's opening Champions League group match at CSKA Moscow a fortnight ago.
He helped his side to a 2-0 half-time lead, only for the Russians to fight back for a 2-2 draw.
The Mexico international is key to Leverkusen's chances of getting a first win against Monaco at the fourth attempt.
- Score to settle -
"We have a small score to settle with Monaco," said striker Stefan Kiessling after three defeats and a draw with the club from the tiny principality in recent years.
Hernandez's hat-trick at Mainz proves he is back to his best, according to Schmidt.
"He wasn't fully fit, but now he's back on top form. It also helped him that he had a strike partner in the closing stages when Stefan Kiessling came on as that gave him more room to operate," said Schmidt.
"He doesn't hesitate when he gets a chance."
He certainly didn't when the chance came along to bag the winner two minutes into injury time.
"I am obviously very happy, but my thanks go to my team-mates, who had a big game," said Hernandez.
"We had some luck, but the late goal was a reward for that hard work."
The victory was important after two recent set-backs, for both Leverkusen and Chicharito.
He missed a penalty in their 2-1 defeat at Eintracht Frankfurt ten days ago and then failed to score in last Wednesday's goalless draw with Augsburg.
With four league goals this season, he is just one behind Borussia Dortmund's Pierre-Emerick Aubameyang and Bayern Munich's Robert Lewandowski amongst the Bundesliga's top scorers.
"He certainly did not win all his battles, but he won the important ones. That demonstrates his wily ability to know where the ball should go," said Leverkusen's director of sport, ex-Germany international Rudi Voeller.
Chicharito's stats in Mainz speak volumes: he scored three goals and hit the post with his four attempts.
"I don't know anybody who is as good as he is in front of goal," marvelled Leverkusen's Germany forward Kevin Volland.
Signing the Mexican international was a big coup for Bayer.
Hernandez has already played in a Champions League final, when his Manchester United team lost 3-1 to Barcelona in the 2011 showcase at Wembley.
Leverkusen have yet to progress further than the last 16 of the Champions League since losing the 2002 final to Real Madrid.
But with the 'little pea' in their ranks, Leverkusen have big ambitions.