The 21-year-old, who spent last season on loan at Rayo Vallecano, used the term when wishing the England international luck as he headed to Poland for Euro 2012 on Wednesday.
He tweeted: "@glen_johnson good luck negrito!!!!"
The Uruguay international unsuccessfully argued "negrito" was not a derogatory term in the Spanish language, despite its racial connotations in English.
When Pacheco received a couple of critical comments in response to his message he wrote: "I Allready (sic) explained in past what Negrito could mean. Good or bad depends how you say it. I always called @glen_johnson it in terms of love.
"Last tweet about it. @glen_johnson speaks Spanish and he knows what that mean when I say it to him. He is one of best mates there for me."