But his nation are not happy with the situation and have even hit back at the Premier League club for 'baring their fangs' over the ace's call-up, despite their apparent error.
Watford have put their foot down and have decided not to release Dennis for the tournament, after the Nigerian football federation sent their request over his late call-up.
Manager Claudio Ranieri revealed earlier this week that Nigeria missed the deadline to inform Watford of their intention to select him.
That gave the Premier League club the power to decide whether or not to release the 24-year-old striker for international duty.
And it has now been confirmed he is staying put in England, with Dennis removed from Nigeria's revised squad list for the finals in Cameroon.
"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," read a statement on Nigeria's official Instagram account, re-posted on the Super Eagles' page.
Dennis has been one of the signings of the season, following his cut-price £3.4million arrival in the summer from Club Brugge.
Previously linked with £25million moves to Manchester United and Arsenal before running down his contract in Belgium, Dennis has proven incredible value for money.
In fact, only Liverpool superstar Mohamed Salah has more goal involvements that the Watford ace in the Premier League this season, with Dennis managing eight goals and five assists in 16 appearances.
Nigeria have been dealt another blow to their squad ahead of their first Group D game against Egypt in Garoua on January 11.
While they will be without Dennis for the tournament, they will also been unable to call upon Napoli top goalscorer Victor Osimhen who has been forced to pull out after testing positive for COVID-19
As per their statement, Nigeria have called up Slavia Prague forward Olayinka, as well as Olympiakos winger Henry Onyekuru to replace the two forwards.
Semi Ajayi from Championship side West Brom and Tyrone Ebuehi, who plays for Serie A club Venezia, have also been added in defence.
Although Watford's concerns have been eased, sixteen Premier League clubs and Rangers are still set to be impacted by the AFCON, which runs from January 9 to February 6.
As many as 40 Premier League players could be called up for duty for the tournament in Cameroon, with Liverpool severely affected by the losses of Mohamed Salah and Sadio Mane during a key part of the season.
In the best case scenario, the players involved could miss at least one Premier League round (weekend of January 15/16), the FA Cup third round (weekend of January 8) and the Carabao Cup semi-finals (w/c January 3 and January 10).
But a run to the latter stages of the tournament could see players miss around a month of action for their clubs.