United play third-tier Wigan on Monday and Cameroon have a friendly scheduled for Tuesday against Zambia before they kick off the tournament against Guinea on January 15th.
"We're talking with the Cameroon federation, it was an issue during the talks with Andre when he came in here (in July from Inter Milan)," Ten Hag told reporters. "It's constructive."
United, languishing eighth in the Premier League nine points adrift of the top four, host fifth-placed Tottenham Hotspur on January 14th.
"I don't know yet (if Onana will be available for Spurs) but he will be here for the game against Wigan," Ten Hag said.
United had a roller-coaster festive period, beating Aston Villa 3-2 with a stunning comeback before a meek 2-1 defeat at Nottingham Forest that kept the pressure on Ten Hag following the takeover of United by Jim Ratcliffe's INEOS group.
Ten Hag met Ratcliffe for the first time.
"We had a long meeting, so many hours we sit together, on many issues we were on the same page, very positive from both sides," the manager said.
"I can say that it was a very constructive meeting and we're looking forward to working with each other."
Ten Hag said it was too early to expect much change to the team under the new ownership.
"We have to let it settle down, they're just coming in, introducing themselves," he said. "They have good ideas, we have to see what we can integrate. In togetherness we will work, but after one day you can't tell that.
"They have given me a few (of their ideas), we have had our debates about strategies and I think we will come together."
United have triggered options on contract extensions for Aaron Wan-Bissaka, Victor Lindelof and Hannibal Mejbri, Ten Hag said, adding that they were "talking with" Raphael Varane and Anthony Martial.
Ten Hag said there was no news on Jadon Sancho's potential loan move to his former club Borussia Dortmund. Sancho has not played for United since late August when he complained about his treatment on social media after Ten Hag criticised his performances in training.
United, eliminated from Europe and the League Cup, have won the 12 FA Cup 12 times, most recently in 2016.
