Despite a normal recovery time of four weeks for the procedure, Uruguay have not ruled out the 27-year-old's participation in football's premier tournament.
"It is very risky to give exact dates. We cannot have absolute certainty or clear numbers but the post-operative period has been very good," Pan said Monday.
"Luis is very positive. I never heard a negative expression and he says it is better every day. Today (Suarez) is painless (and) is working on fitness."
Suarez is understood to have suffered the injury during Liverpool's 2-1 victory over Newcastle, May 11, but the extent of the damage was only revealed after an MRI scan in Montevideo last week.
The 27-year-old's absence would be a huge blow to Oscar Tabarez's team as they aim for a third World Cup title.
Suarez was earlier this month voted the Professional Footballers' Association Players' Player of the Year, having scored 31 Premier League goals in 33 matches.
Uruguay begin their World Cup campaign against Costa Rica in Fortaleza June 14.