La Albiceleste are fifth in the CONMEBOL table, outside the automatic qualification places, following a frustrating 0-0 draw in Uruguay last week.
After that game, Sampaoli offered glowing praise of Messi despite a relatively ineffective performance from the Barcelona forward, but the boss was nevertheless forced to confront claims of a strained relationship with the national team's talisman.
"We live in a society where, when a lie is told a thousand times, it becomes the truth," he told a news conference.
Messi, playing behind centre-forward Mauro Icardi and with Paulo Dybala and Angel Di Maria joining him in attack, found it difficult to have an impact against Uruguay, but Sampaoli has no intention of trying to ease the team's customary reliance on the 30-year-old.
"Messi is fully involved so that Argentina qualify for the World Cup," he said.
"It's difficult to remove the Messi dependency from a team when Leo is there.
"A player like [Ever] Banega, a great enabler, gives Messi the chance to move into the opponent's area.
"The partnerships are there: Leo and Di Maria, Banega and Leo, we're working on Leo and Dybala, Leo and Icardi."
Should Argentina remain fifth, they must negotiate a play-off to secure passage to the finals in Russia next year.
But in a remarkably tight group table, the two-time world champions are only two points behind second-placed Colombia with three matches left, as the destination of the three remaining automatic places behind Brazil look set to go down to the wire.
"Today we have to live with the reality of the table," Sampaoli said. "For me, it's important for us to believe in our own capabilities.
"We have to go looking for the points. We have to get an early goal, that way the opponent has to look for another game plan."
The coach also indicated he could make changes from the side that was held to a stalemate in Montevideo.
"Argentina's formation depends on what we want from the match," he said. "I'm not of the idea of having a starting XI that is set in stone. It's good to have a set of players who are prepared to play."