‘Who is the greatest athlete of all time?’, the question has caused quite a stir on Twitter, and two of the finest sports personalities are under the spotlight. Twitter users started an online battle on Monday debating over who between Lionel Messi and Serena Williams was the greatest athlete of all time.Barcelona fans – referring to themselves as ‘Messi FC‘ – slammed and trolled actress Gabrielle Union who said that the tennis star was the best athlete in the world, and far superior to the little Argentine. A Messi fan had responded to Union’s tweet that said Serena was the greatest athlete of all time saying ‘you have spelt Messi wrong’.Also read: 4 times Messi proved he is the GOAT To this, the actress then quote replied that “When Messi gives birth, almost dies and comes back to dominate lemme know”. This triggered the ‘Messi FC’ who came into their superstar’s defence and trolled the actress for her remarks.One Twitter user called Union’s remarks ‘stupid’ and said that both athletes were legends in their rights and comparisons were uncalled for, especially when they come from two completely varying worlds. Serena is Serena. LegendMessi is Messi. LegendSerena is a woman. Women get pregnant Messi is a man. Men don't get pregnantUsing "when Messi gets pregnant" as a way of rating Serena over Messi is the most stupid thing ever.— Wiz (@Uc_Wiz) September 9, 2018Another Twitter user said the same thing. Serena is no doubt one of the GOAT athletes, but to call her THE GOAT athlete just because she's had to overcome things that the likes of Messi scientifically cannot, is wrong. Judge on an individual basis. Messi is the GOAT player having played in the most popular sport ever.— Dharma Bhagalia (@Kloppholic) September 9, 2018A user also responded by saying that Messi had to go through so much to achieve what he has achieved during his career and that the Union’s comments were ‘disrespectful’.Messi grew up with a growth hormone deficiency, stuck needles into his leg every day for over 3 years, left his family and relocated at 13 years old, then went on to become the greatest footballer of all time.But Serena gave birth. https://t.co/tnWVw6XJRe— Ali (@shotsofthexo) September 9, 2018Even Ronaldo fans came to Lionel Messi’s defence.When Serena Williams is born with a health defect and has to take injections just so he can grow up, and then manages to dominate world football along with Ronaldo for 11 yrs+ lemme know, I prefer Ronaldo but this is blatant disrespect to what Messi has gone through. https://t.co/wUII4IZHcs— Libero (@SW_Libero16) September 9, 2018‘Messi can not give birth, but can Serena do…’Unrealistic argument. Messi cannot give birth, hence we will never know if he can or cannot do it but If Serena can make Jerome Boateng sit on his ass and chip Manuel Neuer from 1 meter away then i will believe you.— Sam (@gphuyel) September 8, 2018Some even linked the actress’ tweet to Serena’s recent tantrums at the US Open final.Hearing Serena Williams "GOAT athlete" shouts and disrespect to Messi, on the same she threw temper tantrums on Center Court of the US Open Grand Slam finals, and lost to a 20 year old rookie from Japan.pic.twitter.com/MwNvOucchn— Rohan (@Rohandinho_) September 9, 2018While others did a poll to decide things, which Serene seems to have won by a pretty huge margin.Let's end this argument, who's the greatest athlete of all time (GOAT).RT for Lionel MessiLike for Serena Williams pic.twitter.com/g6a2v0YRs0— Phoenix (@Sasha_tarky) September 9, 2018Despite the Twitter war of words between the two fandoms, it is pretty much clear that both Serena Williams and Lionel Messi are two of the greatest athletes in the world of sport.Both have gone through ups and downs in their career, and both have had to dig deep at times. One can not discredit their hard work, dedication and work ethic. Both are GOATs in their own right.