Veron's astuteness brought Estudiantes their early goal, scored by Diego Galvan, at La Plata on Thursday night, but the playmaker was replaced at half-time suffering from a niggling right thigh muscle problem.
"I don't know what the heck is the problem," an irritated Veron told reporters in La Plata on Friday after treatment from the club's medical staff amid worries he might not make it to next Wednesday's return leg in Montevideo.
The Argentine side, winners of the trophy three years in succession from 1968 to 1970 with Veron's father Juan Ramon as their outstanding player, also have injury worries in defence.
Estudiantes, shorn of three defenders through injury, were allowed to draft central defender Rolando Schiavi of Newell's Old Boys, who signed a deal for $100,000 to play up to four matches for them if they reach the two-leg final.
The experienced 36-year-old, winner of the trophy with Boca Juniors in 2003, had a good match on Thursday despite only one practice with Estudiantes, and was close to scoring at a corner.
However, left back Cristian Cellay, passed fit at the last minute on Thursday, is doubtful again after suffering a knock and being substituted in the second half.
"We're having quite a few setbacks in this Libertadores Cup," said coach Alex Sabella, who played for Sheffield United and Leeds United 30 years ago.
He said none of Thursday's injuries was very serious but "the bad part is that there are only six days to the return".
Nacional, who lost their unbeaten record in the tournament, are optimistic that they can overcome Estudiantes and reach their seventh final in search of a fourth title.
"No one came here (to La Plata) to lose, but we knew we were playing very difficult rivals. In any case, I think the tie is open," the Uruguayan team's goalkeeper Rodrigo Munoz, told reporters.
"I'm confident we'll turn it around at home," added Munoz, who in the 89th minute stuck out a foot to prevent a second Estudiantes goal, a save coach Gerardo Pelusso said "smelt of qualification."
