Fifa's decision to play the 2021 Club World Cup in June and July could "kill" the Africa Cup of Nations, says Togo coach Claude le Roy.
Set to take place in China with an expanded 24 teams, the club tournament's new timing and format pose problems for Africa's showpiece event.
Cameroon is due to host the next Afcon finals in June and July 2021.
"It's terrible for the projection of this beautiful competition - the Nations Cup," said Le Roy.
Speaking to BBC Sport Africa, the Frenchman - who has coached at a record nine Afcon finals, winning the tournament with Cameroon in 1988 - added: "Fifa's decision that June is a good time to host the Club World Cup means they are killing the Nations Cup."
Two years ago, the Confederation of African Football (Caf) chose to move the Nations Cup from its long-standing January-February slot to June-July - primarily to avoid repeated club-versus-country rows.
But now, European clubs who were unhappy about having to release players in the middle of a season may have to confront similar issues.
If the threat of a European boycott is averted, eight clubs from that continent will line up for the 2021 Club World Cup, as well as three from Africa.
While the final format is still to be decided, reports suggest the European teams could feature the winners of both the Champions League and Europa League from 2018 to 2021.
Meanwhile, the three African teams are set to come from both the finalists of the African Champions League, as well as the winners of a play-off between the losing semi-finalists.
With these varying sides likely to feature many African internationals, Nations Cup club-versus-country battles are set to return.
Yet they can only reappear every four years rather than two, since the revised Club World Cup will be a quadrennial event as opposed to the Nations Cup's biennial nature.
"The Club World Cup has an exclusive window in the international match calendar, so a balanced solution will be found and the dates will be compatible," a Fifa spokesperson told BBC Sport Africa.
"The participation model to determine the clubs that qualify from each confederation will be finalised in a consultation process between Fifa and the six confederations.
"The format will be confirmed in due course."
A Fifa Task Force report into the newly revised Club World Cup mentioned moving the 2021 Nations Cup kick off to July - namely, after the former has ended.
But this move would bring its own problems, because players involved in the Nations Cup contingent would then miss their clubs' crucial pre-season preparations, which intensify that month before the start of many European domestic leagues in August.
"If you move the Nations Cup to July, it's worse than before [when played in January-February] for the clubs," said Le Roy.
"The players will miss the pre-season preparations with their clubs and this part of the season is the most important for the players because of the new season."
"If we transfer a little bit later in July, not one player will be coming back for the pre-season preparations and they will rest for 1-2 weeks and begin the season later than the whole players."
Managers often talk of the importance of the pre-season to a campaign.
Meanwhile, other stakeholders in African football share concerns.
"It's not a good time to play the Club World Cup," Khaled Mortagy, a board member with Africa's record club champions Al Ahly of Egypt, told BBC Sport Africa.
"Even from a marketing perspective, they have to co-ordinate big tournaments with all associations in order to maximise profit."
The BBC has contacted Caf, whose income is largely derived from the Nations Cup, for comment on the scheduling of the 2021 Club World Cup but has yet to hear back.
Fifa's role in the timing has also been questioned by Le Roy.
Fifa president Gianni Infantino was helped into power by African votes and has often spoken of his desire to help the continent.
However, Le Roy criticised the gap 'between the speeches of Infantino explaining that Fifa is here to help Africa and the reality off the field'.
In August, Fifa sent its own Secretary General - Fatma Samoura of Senegal - to take up an unprecedented 'General Delegate' for Africa role in a bid to improve Caf's governance.
"Since Africa is under the supervision of Fifa, do you think that Africa can have a real impact in decisions of world football?" asked Le Roy, who has led Congo, DR Congo, Ghana, and Senegal as well as Togo to Nations Cups.
"I love football more and more as a game but I hate more and more the world of football."
Last week, Fifa confirmed that the 2021 Club World Cup will take place in China.
The 2019 and 2020 editions will remain as annual seven-club tournaments, featuring the various continental champions as well as the local one from host nation Qatar.