But, Liverpool boss Jurgen Klopp was confident that the Senegal international would prove his worth.
As quoted by This Is Anfield, the German said the following back in 2016: “I have followed Sadio for a lot of years since his impressive performances in the Olympics in 2012, and then watched his development in Austria and in his time at Southampton.
“Since I came here I have spoken to the staff a lot about him and have always felt he could be a very good signing for us.
“He has a lot of quality, works hard and has a very good goalscoring record.
“When I spoke to him I could tell that he was passionate about joining the club and playing for our fantastic fans.
“I think they will be just as excited about seeing him put on a Liverpool shirt as I am."
There is no denying that Mane has proven his critics wrong. The 29-year-old has gone on to score 111 goals and register 45 assists in 254 appearances for the club's first-team. Mane has also helped Liverpool win five major trophies.
He was even Jamie Carragher's favourite Red at one stage. The former Liverpool defender said that Mane was a machine.
"Even after the first couple of games (2019-20 season), I said Mane, probably along with Raheem Sterling, was possibly the best left winger in the world," Carragher told the club's official website back in 2019.
"I absolutely love him, he's my favourite player at the club. He's brilliant, he's always got a smile on his face, always there, always gets knocked about, gets goals, setting others up.
"He's the one who came in at the very start under Klopp, his first real big signing, and I think ever since then he's just been getting better and better. He's just a machine."
Despite that being the case, some Liverpool supporters have been critical of Mane at times this season and believe that his best days are behind him.
The winger is getting on, but he has shown across the 2021-22 campaign that he can still contribute. Mane has found the back of the net 14 times and secured two assists in 36 appearances for the Reds this season. He has also been averaging a WhoScored player rating of 7.23.
The aforementioned figures highlight that Mane is still a very good footballer.
Sure, he doesn't look like scoring 22 goals and registering 12 assists (2019-20) in a season anymore.
However, Mane is still offering Liverpool some quality in the final third. Also, with the likes of Diogo Jota and Luis Diaz joining the club in the past 18 months, there is less of a reliance on Mane.
But, the Senegal international is ageing and only contracted until the summer of 2023, which means that his time at Anfield could be coming to an end. We would not be against the club extending Mane's deal.
As we have stated, he is still contributing. Also, Klopp has given Mane plenty of opportunity this season, which does suggest that he still rates him highly.
Then again, if Mane's time at Anfield was to come to an end sometime in the near future, he will always be remembered as a legend of the club.
The forward has helped take Liverpool back to the top of English and European football. You can't ask for much more.
Only time will tell how much longer Mane has at Anfield. We wish him all the best going forward. Mane deserves nothing less.