Porto have confirmed that defender Maxi Pereira was forced to undergo surgery after being injured by a Daniele De Rossi challenge in Tuesday's Champions League play-off clash with Roma.
De Rossi was issued a straight red card after catching the 32-year-old on his shin when attempting to charge down a clearance during the first half of Porto's 3-0 victory at the Stadio Olimpico.
Pereira, who was pictured leaving the stadium on crutches, was consequently forced to withdraw from Uruguay's squad for the World Cup qualifiers against Argentina and Paraguay next month, with Jorge Fucile called up as his replacement.
Porto, who triumphed 4-1 on aggregate against Roma to seal their place in the group stages, have since said that an operation to fix Pereira's damaged tendon has been successfully carried out.
"Uruguayan defender Maxi Pereira's right leg was on Wednesday operated on after he left the field of the Olimpico due to injury on Tuesday," a Porto statement said.
"After closer inspection, we learned the extent of the injury of the Dragaos' number two: a wound with a dislocation of the posterior tibial tendon.
"The operation took place at the Santa Maria hospital and was performed by professor Leandro Massada."
Pereira is expected to be sidelined for a number of weeks.
Roma were eventually reduced to nine men during Porto's 3-0 victory, after substitute Emerson Palmieri was sent off for a dangerous challenge on Jesus Corona.