The Spaniard - currently out with a hamstring injury - arrived from Villarreal in the January transfer window and has been used sparingly by Arsene Wenger, making three appearances in all competitions since his move.
He comes into an Arsenal side that have improved defensively of late - conceding just twice in their last five games - with McLintock hopeful the competition will see an improvement from German World Cup-winner Mertesacker.
When asked about Arsenal's increasingly stoic defence, McLintock told Perform: "It wouldn't be harder to be tighter at the back.
"Mertesacker obviously has a lot of caps and he's been a wonderful player for Germany, but he's not had his best season.
"That might be because of the World Cup. I don't know, I've never played in the World Cup, it's difficult to understand how much that takes out of you.
"He hasn't been at his best, although he played well [against West Ham] on Saturday, and the new boy Gabriel has come in but he hasn't really been tested out a great deal.
"He looked mobile, put in a fantastic tackle a couple of weeks ago [against Everton] so I like the look of him. He's got to have the time to settle down as that was a position that was causing us a problem.
"We lost [Thomas] Vermaelen [to Barcelona] and why we didn't replace him I'll never know.
"We should have had a ready-made replacement and hopefully Gabriel can be the guy."
