Mascherano was heavily linked with a move to Barcelona this summer after two seasons at Anfield and the club's sporting director, Txiki Begiristain, alluded earlier this week to his intention to seal moves for the Argentine and Cesc Fàbregas, the Arsenal captain, next summer.
The Liverpool manager spoke to both Begiristain and Pep Guardiola, the Barcelona manager, over the summer, but no bid was formally lodged, and sources at Liverpool believe the Catalan side would not have been able to match the £40 million Benítez would want to part with the player.
Even with Barcelona hovering, though, Benítez is adamant he will not be corralled into handing improved terms to Mascherano, whose deal expires in 2011.
This follows a summer in which his commitment to Liverpool was questioned and an unconvincing start to the season interrupted by a call-up to help his national side in their hour of need.
"He is a key player for us and will be during the season," said Benítez, who insisted that Mascherano, still recovering from a pelvic injury sustained on international duty, has been "working really hard in training" since returning from Argentina last week.
"He has two more years left on his contract and we would like to keep him," he added. "If we need to talk to him, we will, but he has enough time and he has to play to the level he was before and we will be pleased with him.
"It was difficult for him at West Ham and I remember when I met him he was a little bit low, but as soon as he saw the possibility of coming here he was really pleased. Since then, since his first day, his commitment has been really good.
"Javier has been good for the club and we have been good for him. Thanks to Liverpool he is captain of Argentina, and we have to have the best from him if we want to win more games."
Mascherano is likely to replace Lucas Leiva for Saturday's trip to Upton Park, while Gianfranco Zola will hand Alessandro Diamanti, his £6 million signing from Livorno, his first start.
The West Ham manager will look to the 26 year-old to replace Dean Ashton, who remains unfit after almost a year out through injury.
Lucas Neill, the former West Ham captain, admitted on Friday he was "overwhelmed" by the interest shown in him from Atletico Madrid but insisted he was "delighted" to join Everton on a free transfer.