El Salvador coach Albert Roca is a Spaniard who spent five years at Barcelona as an assistant to Frank Rijkaard.
During his time at Camp Nou, between 2003 and 2008, Roca was able to witness Messi's emergence and development into one of the world's leading players.
Roca is quoted by ESPN Brasil as saying: "I was lucky to be three or four years with him when he began to come to the first team.
"Practically we are talking about the best player of all history.
"It will be a dream to see him again. Even if having to face him is never pleasant."
Messi was considered a doubt for the game against El Salvador after sustaining a blow to his right foot in Barcelona's 2-1 victory over Real Madrid on Sunday.
However, scans showed the player had not suffered an injury and he is was expected to be free to play a part in Saturday's match and Argentina's subsequent friendly with Ecuador in New Jersey three days later.
The Argentine Football Association (AFA) have since confirmed he was forced to miss a training session on Thursday, meaning he remains a doubt for Saturday's encounter.
These two matches, together with a June friendly against Bolivia, offer coach Gerardo Martino - another former Barca employee - the opportunity to fine-tune preparations for the Copa America, which begins in June.
Martino initially named a 22-man squad comprised solely of foreign-based players, before adding Ramiro Funes Mori of River Plate, Independiente's Federico Mancuello and Newell's Old Boys midfielder Maxi Rodriguez to his group last week.
Argentina have played five friendly fixtures since losing the World Cup final to Germany last July, winning three and losing two.
Their most recent outing was a 1-0 defeat to Portugal at Old Trafford in November.
El Salvador, 87 places behind Argentina in Fifa's world rankings, are also playing for the first time in more than four months, having ended a run of four straight defeats with a 2-0 triumph over Nicaragua last time out.
The likes of Messi, Carlos Tevez and Sergio Aguero can be expected to provide much a stiffer examination of Roca's largely inexperienced squad - in only the second meeting between Argentina and El Salvador.
Argentina ran out 2-0 winners when the two teams met in the group stage of the 1982 World Cup.