The Hammers travel to South Wales on the back of a six-game winless run having been held to back-to-back 0-0 draws against Stoke City and Manchester United.
But Slaven Bilic's side could easily have come away from those games with six points, had Zarate had his shooting boots on.
The skillful striker is something of a marmite figure among West Ham fans. Many love watching him in action and he brings a certain flair to the East Londoners' attack.
But others feel he does not pass enough and in recent games has missed some gilt-edged chances to help his injury-stricken side rediscover that winning feeling.
At Old Trafford the Agrentina-born Chile international could and probably should have had at least a brace while against Stoke he twice hit the post.
It has been frustrating for player, manager and fans alike but Swansea be warned, the former Lazio and Inter Milan forward seems to have found his form in front of goal now that the Hammers have switched training grounds from Chadwell Heath to Rush Green.
In a post on the club's official Twitter account, West Ham were keen to give Zarate a boost, showing off his impressive finish.
It got a big cheer from his teammates who will be hoping it helps his confidence ahead of the match against the Swans on Sunday.
The club posted on Twitter: "Mauro Zarate produces an impressive finish as the squad settle into their new surroundings at Rush Green."
West Ham United FC (@whufc_official) December 14, 2015
Zarate had been kicking his heels on the Hammers bench until the injury crisis gave him the chance to shine as a first team starter.
He scored a majestic free-kick against West Bromich Albion last month but has blown hot and cold since getting his big chance.
The 28-year-old forward has a career record of one goal every three games so given his performance in training and the fact he hasn't scored for the last two matches Swansea beware.