Bayer Leverkusen coach Xabi Alonso hailed his former club Liverpool as "one of Europe's best" as he prepares for his Anfield return.

Alonso, who spent five successful years at Anfield and helped Liverpool win the Champions League in 2005, returns to his former stomping ground when Leverkusen take on the Reds on Tuesday.

Arne Slot has won 12 of his first 14 matches in charge of Liverpool, including all three in the Champions League so far.

Leverkusen have only won one of their 11 away major European matches in England (D3 L7), and have lost their last two visits to Anfield, and Alonso is under no illusion as to the scale of the task that awaits the reigning Bundesliga champions.

"For us, it is a big challenge," he said.

"Liverpool at the moment are one of the best, if not the best, in Europe, they are showing that in the Premier League and Champions League, a good squad, great coach. We're looking forward to it. Let's see what happens.

"You can play 70 minutes great but in 20 minutes it [the game] is gone, so it is mentally and emotionally we need to be ready.

"In all areas, they are really strong, so the process works really well. [Slot] has done a fantastic job in three months."

Alonso played 210 times across all competitions for Liverpool between 2004 and 2009, scoring 18 goals and providing 20 assists. 

After winning the Champions League with the Reds in 2005, he helped them reach the final in 2007, though they lost to Milan on that occasion.

However, the Spaniard does not think he will have too much time for a trip down memory lane.

"Unfortunately, there is no time for tourism – maybe a little run or walk," he said.

"I know the city very well, I love it, but tomorrow I will focus on the game and only the game.

"It feels great to be back here after a few years. It's always special. You notice the development of the club; the new stand looks amazing.

"It is a big game against Liverpool, it cannot get much better than that."

The omens are not great for Leverkusen, though.

Liverpool have lost one of their last 21 European meetings with German opponents (W14 D6), albeit that one defeat came against Leverkusen in 2002.