Ole Gunnar Solskjaer said Manchester United will have to reduce their centre-back options if they prise Harry Maguire from Leicester City.
United have been linked with Maguire throughout the off-season, reports claiming the Red Devils are close to agreeing a world-record fee for a defender.
Solskjaer has an array of options in the centre-back area, with Victor Lindelof, Eric Bailly, Chris Smalling, Phil Jones, Marcos Rojo and Axel Tuanzebe all on tour in Australia.
When asked about his stockpile of defenders, Solskjaer told reporters in Perth on Tuesday: "Of course, there's a limit of players.
"Whoever performs will be part of the team and whoever doesn't has a fight to get back in.
"There's been loads of speculation but I can't really say anything.
"We'll work to find a relationship with the ones we've got."
Tuanzebe, 21, is back with United following an impressive loan spell at Aston Villa, who he helped secure promotion to the Premier League last season.
Solskjaer, who confirmed Fred, Matteo Darmian and Dean Henderson will join the squad for the next part of their pre-season tour in Singapore, added: "Axel has got a great chance of staying here and playing. He had a great season last year.
"It was a stop-start season with injuries, but he's really proven that he is capable of playing at that level, he got promoted with Villa and he's come back very strong, focused.
"He did well in the first game here, so he's one of the young, exciting players that I can't wait to see more."
United will face rivals Leeds United in Perth on Wednesday following their 2-0 win over Perth Glory on Saturday.