Manchester United number two Carlos Queiroz believes contracts are becoming meaningless in the ongoing transfer saga surrounding Cristiano Ronaldo.
Ronaldo, 23, has been publicly courted by Real Madrid throughout the close season with reports continuing to suggest the Spanish giants will ultimately sign the Portugal international for a world record transfer fee.
Queiroz has urged the winger to remain at Old Trafford and the Red Devils are adamant their 42-goal top-scorer from last season is not for sale.
Ronaldo still has four years remaining on a long-term contract signed last summer, but Queiroz has admitted that it is no guarantee the player will stay in Manchester.
"Contracts are becoming meaningless in football, for players and managers," he said.
"It is a now often a case of dog eat dog."
Meanwhile, Queiroz has played down fresh speculation linking him with the managerial vacancy with the Portugal national team.
Luiz Felipe Scolari's decision to take over at Chelsea following Euro 2008 has left Queiroz the firm favourite for the post.
"I've been in the game too long to plan with any certainty beyond today," he continued.
"But in all likelihood I will be in South Africa next month with United for their pre-season tour."