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FRANCEVILLE, Gabon -Four-time African Cup of Nations champion Ghana is an overwhelming favorite to beat first-timer Botswana in the opening round of matches in Group D on Tuesday, even if the country's vice president is worried about an upset.

John Dramani Mahama warned Ghana's players at their training camp in Gabon that they should avoid complacency against underdog Botswana, which also will be weakened by injury on its debut.

Ghana has to do without suspended defender Isaac Vorsah in Franceville, but the inexperienced Botswana squad will seriously miss forward Joel Mogorosi, who broke his arm at training last week just before the team traveled to the tournament.

Injury problems were also mounting for Mali coach Alain Giresse before the Eagles face Guinea in the second match at Stade de Franceville on Tuesday, with doubts over Barcelona midfielder Seydou Keita and striker Cheick Diabate.

"We will do whatever it takes to get the best performance,'' said Giresse, who had already been forced to alter his plans after Toulouse defender Mohamed Fofana and midfielder Kalilou Traore were withdrawn from Mali's squad with injury.

Even without Vorsah, Ghana is expected to still be too good for a Botswana team that surprised many by qualifying for its first African Cup. The Black Stars were visited at training on Sunday by Mahama, Ghana's football association said, with the team attempting to end a 30-year title drought at the African Cup.

"Every country came to this tournament on merit so you should avoid complacency,'' Mahama told the players.

Ghana said every squad member apart from Vorsah was available for its opening game, including striker Asamoah Gyan, who had been in a race to recover from a hamstring injury in time for the start of the tournament.

Coach Goran Stevanovic may still choose to rest Gyan against Botswana, however, with brothers Andre and Jordan Ayew of Marseille and Prince Tagoe all capable of filling in up front and Ghana probably facing tougher tests later against Mali and Guinea.

After Senegal fell to Zambia in its opening game and Ivory Coast was pushed hard by Sudan, the tournament has already seen strong performances from underdogs following a qualifying competition that produced a string of upset results. Botswana may be at its first major competition but it also qualified ahead of former champion Tunisia and Togo, while Ghana is under pressure to deliver a long-awaited success.

"The expectation is high and we know it won't be easy but we're hopeful and believe we can win it,'' Ghana captain John Mensah said. Seydou's absence against Guinea after reported knee and ankle problems would be a blow to Mali's hopes of making a strong start and challenging Ghana as Group D's top team.

The experienced midfielder is to guide a new generation of Mali players at the tournament in the absence of former stars like striker Frederic Kanoute and midfielders Mahamadou Diarra and Mohamed Sissoko, who no longer play international football.

"It's not an easy group, it's a difficult group,'' Giresse said. "(But) we want the best. We want the maximum.''

The renovated stadium in Franceville, in the south east corner of Gabon, will be the fourth and final venue to feature at this year's African Cup of Nations.