If we win, we go eight points clear and that's the intention.
Atletico is one of Messi's favourite opponents in La Liga as the Argentine has scored 27 times in 35 meetings against the team from Madrid.
Atletico is four points behind the Catalan club, which visits Las Palmas on Thursday to try to regain a seven-point lead.
Griezmann will enter Sunday's game at Camp Nou boosted by two outstanding performances in the last two league games.
"We are going through a great moment", Simeone said.
Pogba and Griezmann play together for France and United are convinced their record-signing will come to life with his global team-mate playing in front of him.
Atletico Madrid manager Diego Simeone has insisted Barcelona superstar Lionel Messi "cannot be controlled", as he prepares to take his side to the Nou Camp on Sunday for a top of the table clash.
Atletico, too, had a goal ruled out as they sought an equaliser that would have at least kept them on Barca's coattails.
Jose Mourinho has already denied United will look to spend big on another attacker this summer, but the club is believed to be desperate to partner Paul Pogba with Griezmann.
Griezmann, who reached 100 goals for Atlético when he scored a hat-trick against Sevilla last weekend, has been strongly linked with a move to Barcelona at the end of the season.
"I'm trying to make the fans happy", he said after the Leganes match. For Atleti to close the gap on Barcelona, they need their league-best defense shut down Messi and Suarez and have Costa or Griezmann find the back of the net.
The Atletico boss, who welcomes back defender Lucas Hernandez into his squad following injury, added: "Valverde resolved the departure of Neymar, changed a system that had worked successfully for many years, taught everyone that Barcelona can also play 4-4-2 and he's unbeaten in the league".
"I'm very happy here, and so is my family, and in the end that's the most important thing" he said.