A Nigeria Football Federation (NFF) statement said Dennis had been excused because Watford were "baring fangs".

Osimhen has been ruled out following a positive Covid-19 test and is still recovering from facial fractures.

The injury in November was expected to rule the Napoli frontman, 23, out of the tournament, which starts on 9 January in Cameroon.

Dennis, 24, will now be available for Watford's league games against fellow strugglers Newcastle and Norwich, as well as their FA Cup third round tie at Leicester City on 8 January.

Watford manager Claudio Ranieri said: "I knew the board and Nigerian board were speaking. I accept every decision they find and that for me is finished."

Asked whether the decision for Dennis to remain with his club disrespected Afcon, Ranieri added: "No. They have a lot of players and then they changed the managers and everything. We were ready to give over the players, they didn't do it. The two boards spoke and for me it is OK.

"Of course he wanted to go to play but he also wanted to help Watford."

Dennis and Osimhen have been replaced by Sparta Prague striker Peter Olayinka and Olympiakos forward Henry Onyekuru, while the Super Eagles have also been forced to make two changes in defence.

Rangers defender Leon Balogun and Cyprus-based Abdullahi Shehu have both been replaced by West Brom's Semi Ajayi and Tyronne Ebuehi of Italian Serie A side Venezia.

Super Eagles hit by Covid and administrative issues

Dennis was not part of Nigeria's initial 37-man provisional squad submitted by former coach Gernot Rohr, but added to the 40-man party in December.

His inclusion in the final squad led to Watford manager Claudio Ranieri revealing the club could refuse to release him.

Ranieri said Nigeria missed a deadline to advise the Premier League club that the forward was being considered for selection.

BBC Sport Africa understands the NFF conceded it may have left it late and is now in a weakened position to request Dennis to travel.

"In-form rapid raider Emmanuel Dennis, whose English Premiership club is baring fangs, has been excused to provide room for Czech Republic-based forward Peter Olayinka," Nigeria's official account said on Instagram.

Despite being keen to travel to Cameroon for the continental showpiece, Osimhen officially informed interim coach Augustine Eguavoen about his decision to withdraw on Thursday.

His latest coronavirus problem and Napoli's reluctance to release him for the tournament led to the player sending an official letter.

"He just felt he was not in the right of mind, physically and psychologically, to play for Nigeria with all that is going on right now," a leading NFF official told BBC Sport Africa.

The three-time African champions, who have appointed Portuguese Jose Peseiro as their permanent coach, are in Group D along with Egypt, Guinea-Bissau and Sudan.

They open their campaign against the Pharaohs in Garoua on 11 January.

More Covid cases as Choupo-Moting awaits scan results

Bayern Munich's Eric Maxim Choupo-Moting is a key player for Cameroon

Meanwhile, Cameroon forward Eric Maxim Choupo-Moting has suffered an injury scare and the hosts are the latest to announce several coronavirus cases.

Choupo-Moting, 32, is awaiting the results of a scan after he left a training session early because of a knee issue.

The Cameroon Football Federation said Pierre Kunde Malong, Jean Efala, Michael Ngadeu Ngadjui and Christian Bassogog had been under observation since Wednesday because of "strong suspicions" they had the virus, and the quartet will continue to quarantine.

The Indomitable Lions face Burkina Faso in the first game of the tournament on 9 January.

Fellow Group A contenders Cape Verde have had seven players

- including all three goalkeepers - and an assistant coach test positive.

Holders Algeria and Ivory Coast have also reported cases at their training camps in Qatar and Saudi Arabia respectively.