Havertz suffered a torn hamstring during the Gunners' training camp in Dubai and will require surgery, which will end his season prematurely.
The Germany international joins Bukayo Saka, Gabriel Jesus and Gabriel Martinelli on the sidelines for Arsenal, who trail league leaders Liverpool by seven points.
It leaves Mikel Arteta with Leandro Trossard, Raheem Sterling and Ethan Nwaneri as his only attacking options, making the decision not to bring in January reinforcements ill-judged.
Here are five free agents Arsenal could pursue to extinguish the fire breaking out up front.
Lucas Perez
We start with a former Arsenal player in Lucas Perez – if you can really call him that – as one route to addressing current forward concerns.
Perez had a forgettable spell for Arsenal between 2016 and 2018, making just 21 appearances and scoring seven goals.
He didn't pull up many trees during a spell at West Ham either but his numbers in Spain are good, particularly at Deportivo La Coruna where he has 75 goals and 56 assists in 237 outings.
Now aged 36, Perez is a free agent after terminating his Deportivo contract in January for personal reasons.
Mariano Diaz
Without a club since the end of last season, Mariano Diaz appears as more of a wildcard given his numbers across two separate stints at Real Madrid.
Often a deputy, the Dominican never really made a name for himself at Real, either side of a fruitful season at Lyon where he scored 21 goals.
Diaz does have an impressive resume boasting two Champions League and three La Liga titles, although they may need to be looked at with a pinch of salt...
Maxi Gomez
Maxi Gomez has 32 Uruguay caps under his belt, but it clearly isn't enough to prevent him from hitting the free-agent market.
Gomez was prolific earlier in his career at Celta Vigo which earned him a transfer to Valencia, where his scoring numbers dropped.
Trabzonspor was his next calling for a season before an ill-fated loan spell at Cadiz last term, which yielded zero goals in 33 appearances.
So it seems Gomez has forgotten where the net is, but he used to know where it stood.
Carlos Vela
Another former Arsenal man, Carlos Vela has made his mark on football away from the Gunners, despite previously being contracted to the club for seven years.
It was on loan then permanently at Real Sociedad where the Mexican found his groove before he upped sticks to join Los Angeles FC in MLS.
Vela enjoyed six years in the United States scoring 93 goals in 189 appearances and earned the MLS MVP of the Year in 2018.
A return to north London does look to be far-fetched for Vela, but this is a player who has elevated his game as his career has gone on.
Diego Costa
Last but by no means least, could battle-hardened Diego Costa be the solution?
A two-time Premier League winner with Chelsea, Costa would need no adjustments for a third return to England after also having a brief spell at Wolves.
Costa has always been a bit of a handful but it does look like his best days are past him, as demonstrated by his one goal in 25 outings for Wolves.
It would carry on a bit of a recent trend of Arsenal signing former Chelsea players, but even this one seems a bit of a stretch.