But Sydney FC's attacking midfielder, who has played 40 times for Poland, has taken the competition by storm in his first season in Australia.
He has played a key role in the Sky Blues' retention of the Premiers' Plate and helped main striker Bobo score the highest number of goals in a season.
So it is quite fitting that Mierzejewski has become the red-hot favourite to snare the coveted Johnny Warren Medal.
There would be no more deserving recipient of the player of the year trophy.
In a short time, Mierzjewski struck a formidable partnership with Serbian playmaker Milos Ninkovic and together these two genuine stars from eastern Europe have lifted Sydney to even greater heights than last season's.
The Sky Blues may have won the 2017 premiership more comfortably and accrued more points but there is no doubt that Mierzejewski has added a level of finesse and sophistication to the team's general play that rarely has been seen in Australia.
The Polish predator - who is on a three-year contract but is not even a marquee - came to Australia from Sharjah FC in the UAE and it took him several weeks to regain full fitness and adjust to Australia's pitches and conditions.
He showed glimpses of his class in his first forays but when he hit his majestic stride - after eight or nine rounds - Sydney could see how formidable a player they had acquired.
Surely the club must do everything in their power to keep the influential Pole for the duration of his contract even though his value, according to the respected German website transfermarkt, is a tempting A$4.14 million.
Mierzejewski has played 90 minutes in all but three of Sydney's matches from round nine, and this excludes four games in the AFC Champions League and three in the FFA Cup.
His figures in the A-League are staggering.
In 22 matches so far, he has scored 13 goals and made seven assists: that's almost a goal or an assist a match.
For good measure he also made the winning goal for Bobo in the FFA Cup final against Adelaide United, which the Sky Blues won 2-1 after extra time.
Mierzejewski's impact on Sydney and the A-League cannot be overstated.
He is probably not as 'explosive' as Ninkovic and does not work as hard as the Serb but he is always in the thick of the action, spraying balls across the field with surgical precision and making things happen with flair and regularity.
Mierzejewski's mastery of the ball is immaculate and he has this uncanny ability to put his body between the ball and his opponents, making it hard for them to see it and they will get it only by fouling him. Montenegrin master Dejan Savicevic was like that, too.
Mierzejewski was close to his mesmerising best in the first half of the match against Perth Glory, which Sydney won 3-2 to clinch the premiership and become the first team in A-League history to retain that title.
With the finals coming up shortly, Sydney are well placed to secure the treble.
The Pole opened the scoring after 12 minutes by latching on to a loose ball from close range and stabbing the ball home.
He then came up with a magnificent pass down the middle to Matt Simon before the striker was brought down in the box and Bobo tucked away the subsequent penalty.
He also played in Bobo with a perfect ball from his own half and the Brazilian did the rest from close range.
All this in less than half an hour in the first half.
Graham Arnold, possibly with next week's ACL clash against Suwon Bluewings in mind, gave Mierzejewski and Bobo an early mark in the second half but by then, the two had done the damage and the Sky Blues were able to survive a late burst from the home side that made the score more respectable.
JOHNNY WARREN MEDAL WINNERS
2006: Bobby Despotovski (Perth Glory)
2007: Nick Carle (Newcastle Jets )
2008: Joel Griffiths (Newcastle Jets)
2009: Shane Smeltz (Wellington Phoenix)
2010: Carlos Hernandez (Melbourne Victory)
2011: Marcos Flores (Adelaide Utd)
2012: Thomas Broich (Brisbane Roar)
2013: Marco Rojas (Melbourne Victory)
2014: Thomas Broich ( Brisbane Roar)
2015: Nathan Burns (Wellington Phoenix)
2016: Diego Castro (Perth Glory)
2017: Milos Ninkovic (Sydney FC)