When Stuttgart came out of the hat on December 19 they were 15th in the Bundesliga, with two league wins, and only goal difference stood between them and the relegation playoff spot.
Since then the Germans have jumped to ninth in the table after seven wins in eight games under former Tottenham Hotspur coach Christian Gross and they go into the first leg against Barca full of confidence.
Stuttgart sounded another warning on Saturday when they won 5-1 at Cologne, helped by four goals from Brazilian-born striker Cacau who returned after a month out through injury.
"Now we are looking forward to Barcelona. We need to focus our energy for that one then we can cause an upset," said Cacau, who played four matches for Germany last year and is still nurturing hopes of a World Cup call-up.
"Saturday was a first step."
Gross, who took over two days before their final group stage match against Unirea Urziceni which Stuttgart won 3-1, said: "We're happy to be playing against one of the world's best teams. There's a lot of prestige at stake."
La Liga leaders Barcelona, 4-0 winners over Racing Santander on Saturday, have lost only one league match all season.
GROUP WINNERS
They topped Champions League Group F ahead of Inter Milan but managed only seven goals in six games which included two goalless draws.
Barca captain Carles Puyol acknowledged they would be facing a much-improved side.
"They are doing better," he said. "They are a very dangerous team. If we do not keep our concentration we will find ourselves in trouble."
The Catalans have included Zlatan Ibrahimovic, Daniel Alves and Xavi in their squad but Barca did not say whether the trio would be fit to play.
Ibrahimovic was replaced by Thierry Henry, who scored only his third goal of the season, against Racing.
Probable teams:
VfB Stuttgart: 1-Jens Lehmann; 27-Stefano Celozzi, 5-Serdar Tasci, 17-Matthieu Delpierre, 2-Cristian Molinaro; 35-Christian Traesch, 32-Zdravko Kuzmanovic, 13-Timo Gebhart, 23-Aleksandr Hleb; 18-Cacau, 29-Pavel Pogrebnyak
Barcelona: 1-Victor Valdes; 5-Carles Puyol, 3-Gerard Pique, 4-Rafael Marquez, 19-Maxwell; 8-Andres Iniesta, 16-Sergio Busquets, 24-Yaya Toure; 10-Lionel Messi, 9-Zlatan Ibrahimovic, 17-Pedro
