That’s according to former Arsenal and Aston Villa midfielder Kevin Richardson, who is currently taking charge of the young Magpies.
Munoz – signed on an 18-month loan from Mexican outfit Santos Laguna, which includes an option to buy – missed Friday’s 4-1 Tyne-Tees derby win over Middlesbrough at St James’s Park.
"He's been training and doing running drills to get his fitness up,” Richardson said after the game.
"It's down to the sports science people when he will be introduced to the group."
Munoz, speaking to TUDN in Mexico late last week, revealed: “They train me separately. I have activities with the team but most of the time it’s separated for physical conditioning and getting into the rhythm.
“I have talks with their coaching staff and they will let me know when I’m part of the group.”
United’s second string travel to Harrogate Town on Tuesday evening in their second Papa John’s Trophy group game.
The two sides met in pre-season with the League Two side claiming a narrow 2-1 victory.
Richardson added: "It'll be an experience for the lads, even though we have played them earlier in a friendly.
"It was a good game then. It's against bigger and stronger men.
"It is a good experience, and we done OK last time even though the result didn't go our way.
"There are things to work on and a lot of positives.
"We try to stay positive as much as we can and tweak bits we need to improve on."