The prolific striker suffered the injury during a pre-season clash with Manchester United in July after being wiped out by young goalkeeper Nathan Bishop.
As a result, Mullin was forced off the pitch in an oxygen mask following seven minutes of treatment on the field.
That injury was enough to rule the 28-year-old out of action until early September, however he failed to score in his first three appearances for Wrexham this term.
But after starting the League Two clash with Crewe, Mullin showed that he was back to his glorious best after converting an overhead kick.
A long ball was played in to Ollie Palmer who headed it across the penalty area towards Mullin who improvised a brilliant effort to find the bottom corner.
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Mullin scored 47 goals for Wrexham last term to help them to promotion from the National League.
With hopes of a play-off push in League Two this term, Rob McElhenney and Ryan Reynolds will be praying that the lethal attacker can score plenty of goals to help them fulfill their objectives.
Mullin's goal leveled the game at 1-1, before Crewe scored a penalty just before half-time.
However the striker draw the game level again with a neat effort just three minutes after the break.
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Crewe put themselves ahead for a third time during the second half, however former Wolves and Sunderland man Steven Fletcher spared their blushes with a 95th-minute equaliser for the Welsh side.
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