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The 21-year-old, who has scored nine goals and delivered 10 assists in the Bundesliga this season, was sidelined with an ankle ligament injury in early March.

His return could not have come soon enough for second-place Leverkusen, which is six points behind Bayern Munich with six matches left this season.

"Flo is back fit, he is in the squad, he can play, also from the start and that's very good," Alonso said.

"We are a better team with Florian. We have better connections between the lines. He is the player who makes the difference for us."

Defending league champion Leverkusen has 62 points and is running out of time to catch Bayern, which also beat it in the UEFA Champions League Round of 16.

Leverkusen has won five of its past six Bundesliga games. No side has recorded as many victories and claimed as many points, 15, since the start of matchday 23.

It also have a fine record against Berlin, losing just once in 11 previous Bundesliga meetings and winning six of those.

At home, Leverkusen is unbeaten against Union, winning three and drawing two of those meetings and scoring 14 goals.

Alonso said there was no point looking at the table because it was clear his team needed to win all its remaining matches to have any chance of winning the title.

"It is our task to put pressure on them [Bayern] and then we will see what happens," the Spanish coach said.

If Leverkusen beats Berlin, it would move three points behind Bayern, which does not face Borussia Dortmund in Der Klassiker until later in the day.

Bayern has a busy schedule with a trip to Inter Milan next week for a UEFA Champions League quarter-final second leg after losing the first 2-1 at home.

"Our goal is to win all the matches," Alonso said. "We know this is our only chance.

"We're taking it one game at a time and see what comes out of it. We want to win tomorrow. We want to do our bit."