Lionel Messi, center, scored twice in his return to Barcelona after a two-month injury layoff and returns in time to face La Liga challenger Atletico Madrid on Saturday.
S. Lau/AP

MADRID (AP) - For Atletico Madrid, Lionel Messi has returned at the worst possible moment. And the Barcelona forward is eager to make up for lost time going into what could prove the most important games of the season.

Messi is back from a two-month injury layoff and is available Saturday at the Vicente Calderon Stadium, where Barcelona takes on co-leader Atletico.

Barcelona coach Gerardo Martino's biggest dilemma doesn't seem to be tactical, but whether or not to play Messi from the start.

''He hasn't asked me to start. He's told me he feels in perfect playing conditions,'' Martino said on Friday. ''It's not an easy decision to make because we're talking about the world's best player. And Leo is coming off a long period of inactivity.''

Messi certainly didn't show any lingering effects from a left hamstring injury when he came off the bench to score twice in Wednesday's 4-0 cup win over Getafe.

''What we have to evaluate is if he can play 90 minutes, which we'll decide tomorrow. We're not going to waste all of the work and hours put in by Barca and Argentina's physical trainers, and even by him himself, to get back on the field,'' Martino said. ''When it comes time to decide we'll forget about the opponent and remember that this is not a game being played (at the end of the season) but on Jan. 11. It is a decisive match, but not crucial.''

Curbing Messi's desire to play when injured has been one of Martino's greatest tasks since taking over from Tito Vilanova. Martino suggested Messi will play as a substitute in Madrid.

''Leo likes to starts and finish games, so the best way to keep him calm is to start him on the bench before letting him come on,'' the Argentine coach said.

Atletico coach Diego Simeone was preparing his team for Messi, as well as Neymar who has been cleared to play after picking up a stomach bug.

WATCH: Messi scores twice in return from injury

''Barcelona without Messi tomorrow? We don't believe that. I can't imagine him sitting out the game tomorrow, although it's always a possibility,'' Simeone said on Friday. ''But my players aren't afraid of anyone, and that's key.''

Simeone has maintained a mantra of teamwork and humility as keys to his team's success, qualities the former Argentina international believes helped the club win its last title - in 1996. Only Deportivo La Coruna and Valencia have broken the Barcelona-Real Madrid monopoly since.

''They have a deep squad which includes a lot of different skilled players. I think this Barca is more dangerous than before, it's even better than the one that won (six titles),'' Simeone said. ''It's not a final, it's just another very important league game. We'll just try to play the same way we did against them in the (Spanish) Super Cup.''

Barcelona managed to win that two-legged competition on away-goals, although Atletico emerged with more confidence after the 1-1 aggregate result. Atletico will close the first half of the season with its best ever points total - the two teams are tied on 49 points from 18 games - regardless of the result.

''I said it during the Super Cup that they are a very strong team,'' Martino said. ''To me, Atletico Madrid has not only been one of the most disciplined, well-coached teams in Spain, but in Europe.''

Copyright 2014 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

SI Apps
We've Got Apps Too
Get expert analysis, unrivaled access, and the award-winning storytelling only SI can provide - from Peter King, Tom Verducci, Lee Jenkins, Seth Davis, and more - delivered straight to you, along with up-to-the-minute news and live scores.