Mali coach Patrice Carteron said France-based goalkeeper Mamadou Samassa will start ahead of the more experienced Diakite, from Bamako club Stade Malien, who saved two penalties in the quarter-final triumph over South Africa.
Guingamp goalkeeper Samassa missed the South Africa game last Saturday because of a one-match ban after picking up two bookings in the group stage.
Carteron has praised Samassa, 22, who represented France in age-group sides, but opted for Mali at full international level, making his debut last October.
Mali are hoping to beat Nigeria and qualify for only their second Africa Cup final after losing 3-2 to Congo Brazzaville in Yaounde 41 years ago.
"We will play to win," vowed Carteron.
"We will attack because we want to win without going to penalties.
"Nigeria are favourites, but we aim to beat them. The pressure is on them - we are not under pressure because we are not the favourites."
Former Lyon defender Carteron believes his team must impose themselves physically to reach the final.
"The teams are similar physically and the team who wins the physical battle will win the match," he predicted.
Skipper Seydou Keita wants to improve on the showing at the 2012 tournament in Gabon/Equatorial Guinea, where they went out to Ivory Coast at the semi-finals stage.
"It will be a tough game but we want to win it. This will be our second straight semi-final and we want to go further.
"I have not won a trophy with Mali, but we have a chance now and we hope we can do it."
The Malian squad have given former South African president Nelson Mandela a signed shirt of skipper Keita.
Carteron said they would love to meet Mandela, but this was not possible so they decided to send him a No 12 shirt of Keita signed by the entire squad.