Zenit, Russian champions, are struggling at the start of the new season, lying 10th in the league with just one win and seven points from six matches.
However Bayern, who failed to qualify for the Champions League for the first time in a decade, will be without star striker Luca Toni who is suspended for the first leg at the Allianz Arena in Munich.
The Italy striker, who has scored eight goals in four games, was booked in the thrilling 3-3 quarter-final draw at Getafe when he netted twice in the final five minutes of extra-time to put Bayern through on away goals.
|"We've still got two titles to go. I hope by the end of May we'll have all three."|
Bayern Munich striker
"We won the Cup and now we want the league championship and the Uefa Cup for the treble," Toni told reporters after scoring twice in Saturday's 2-1 victory over Borussia Dortmund, his 34th and 35th goals of the season.
"We've still got two titles to go. I hope by the end of May we'll have all three."
Zenit crushed Bayer Leverkusen in the quarter-finals, winning 4-1 in Germany before losing the return leg 1-0, with Anatoliy Tymoschuk, Ukraine midfielder, expected to return to Dick Advocaat's team.
Rangers rocked by absentees
Meanwhile Rangers, who lead the Scottish Premier League, have been hit by a series of injuries and suspensions for their Uefa Cup semi-final first leg at home to Fiorentina.
Captain Barry Ferguson and fellow midfielder Kevin Thomson are banned, while Allan McGregor, in-form goalkeeper, is among a long list of casualties for the Glasgow club.
Striker Lee McCulloch and midfielder Charlie Adam are out, while Steven Naismith and Chris Burke are likely to miss both legs after picking up knee and ankle injuries respectively in Sunday's Scottish Cup semi-final win over St Johnstone.
"Naismith and Burke have no chance of playing on Thursday and I think they will miss our next three games at least," Walter Smith, Rangers manager, told reporters.
|"I don't think it changes anything playing away first and at home second."|
Fiorentina, who are fourth in Serie A and well in contention for a Champions League place next season, have been luckier with injuries with Tomas Ujfalusi, Czech defender, the only notable absentee due to a thigh problem.
The Italian club managed a 2-0 away win against PSV Eindhoven in their quarter-final after lacklustre 1-1 home draw in the first leg, but defender Dario Dainelli said his side could not take it easier in the semi-final just because they play at home second.
"I don't think it changes anything playing away first and at home second. We always go on the field with the same attitude," Dainelli said.
"We are already very focused."
The second leg in Florence is on May 1, with the Uefa Cup final to be played at the City of Manchester Stadium on May 14.