Atleti are five points behind Lionel Messi et al after Barca were held to a 1-1 draw by Las Palmas on Thursday.
The two sides will clash this weekend at Camp Nou, with Atleti looking to extend an eight-game unbeaten streak in all competitions.
And Mendieta believes the game offers perhaps Atleti's only chance to close the gap as the season progresses.
"It will be a tough game. For Atletico Madrid, it will be about cutting off the points gap, while for Barcelona it will be to keep the distance at the top of the table because the end of the season will be really tough in terms of the title challenge," he told Goal in an exclusive interview.
"Atleti will have this match as the only chance to get closer to Barcelona."
Mendieta spent a solitary season on loan at Barca, but is perhaps best known for his spell at Valencia, where he won the Copa del Rey and the Supercopa de Espana, while he also reached two Champions League finals.
Valencia are currently fourth in La Liga, just one point behind Real Madrid, and Mendieta has been impressed with the current crop of players.
He said: "I think the performance of Valencia so far has been great. Considering the past few seasons, it has been really good.
"What started as a new project, under a new manager and a bit of expectation, it has been amazing. Now, hopefully, Valencia qualify for the Champions League."
Valencia have a remarkable track record of producing major stars, including the likes of David Silva and Paco Alcacer, and gave a debut to talented right winger Ferran Torres earlier this season, with the 18-year-old recording his first assist in the 1-1 draw with Athletic Bilbao.
Mendieta added: "Valencia has always had a great academy. The way they project their youngsters into the first team is great. Ferran Torres is another talented youngster who has come through the academy.
"Valencia has always been a club which has broken young talent through the ranks and sold them. This has been their philosophy all these years; it’s great to see them produce great players."