Conteh played for Guinean side Ashanti Golden Boys de Siguiri and had received several call-ups to Sierra Leone's squad but was yet to secure a place in the international side's first team.
He was part of the Leone Stars 18-man squad for their 2019 Africa Cup of Nations match against Kenya last month but dropped out the night before the match due to poor health.
It's very sad to wake up and hear news like this. Alhaji was such a great person
"Conteh was not impressive in the last day of training because something was wrong with him," Sierra Leone's coach John Keister told BBC Sport.
"I even told one of my assistants about it. This forced me to drop him from the squad. We'll surely miss him. I always liked him because he was humble and always good to be around the Leone Stars team.
"He was a clever boy and had a goalkeeper's height and good goalkeeping abilities," Keister added.
Some of Sierra Leone's biggest international stars have also been playing tribute to their team-mate.
"It's very sad to wake up and hear news like this," said former Norwich city and Middlesborough striker Kei Kamara.
"Alhaji was such a great person; being a college graduate and a footballer is a hard thing to do and he was able to accomplish that. My prayers to his family," Kamara added.
Leone Stars skipper Umaru Bangura spoke of his shock at hearing the news of Conteh's death.
"We've lost a good goalkeeper. We were with him in camp last month when preparing for our match against Kenya. We'll miss him.  Rest in peace Conteh," said Bangura.
Turkey based midfielder Alfred Sankoh also paid tribute to the 25-year-old.
"Rest in peace brother. God knows best but this is so scary after a month when I was with you in the Leone Stars camp."
Former Leone Stars captain Mohamed Kallon, who brought Conteh to his club FC Kallon some years ago, described the goalkeeper as a "great guy with lots of ambition."
"He graduated from college and he was working whilst playing for FC kallon," said Mohamed Kallon.
"He was a talented goalkeeper and it is a great loss for Sierra Leone. May his soul rest in Peace. We love him but Allah loves him most."
Conteh, who is yet to be buried, was one of few educated Sierra Leonean players with a degree having graduated from Fourah Bay college at the University of Sierra Leone.
He played for three Premier league clubs in Sierra Leone - East End Lions, Kallon FC and Diamond Stars of Kono - as well as two clubs in Guinea, Fello Star de Labè and Ashanti Golden Boys de Siguiri.
Sierra Leone is mourning the death of top goalkeeper Alhaji Dauda Conteh who has died from a short illness in hospital in Freetown aged 25.