Messi, 19 in 10 days time, suffered a knock near the end of the afternoon practice and will be under observation overnight, press officer Andres Venrura said, speaking for Villani.
"He'll have it evaluated in the next hours and tomorrow we'll see. If it doesn't hurt we'll forget about it," Ventura said.
Messi only recently recovered from a thigh injury that kept him out of action for Barcelona from the Champions League quarter-finals until the end of the Spanish league season.
Team sources say he is anxious to get off the mark in the World Cup where he has so far sat on the bench during Argentina's opening Group C match, a 2-1 win over Ivory Coast in Hamburg on Saturday.
Argentina play Serbia & Montenegro next in Gelsenkirchen on Friday where Messi looks set to be on the bench again and hoping for the chance to win his eigHth cap.
Coach Jose Pekerman could name his team on Thursday.
The Netherlands complete the group.
