BERLIN, Aug 10 (Reuters) - Bayern Munich start the defence of their Bundesliga title on Friday against Borussia Dortmund needing a vast improvement in attack after failing to score a single goal in four pre-season matches.
The overwhelming favourites have got off to a rocky start in the post-Michael Ballack era, after their dangerous midfielder left for Chelsea in the close season, with three defeats and a League Cup semi-final penalty shootout win after a 0-0 draw.
Coach Felix Magath has remained remarkably unperturbed, at least on the surface, by the sluggish start and warned it could take until the end of August before the half-dozen players returning late from World Cup duties regain their form.
'It's quite possible we'll have some problems with our first matches,' he said after Bayern lost 2-0 to Werder Bremen in the pre-season League Cup final on Saturday.
'But it's only normal after a big tournament like the World Cup. We're still looking to find our rhythm. It's a very long season. We shouldn't get too worked up. We need to stay calm.'
Bayern decided not to buy a replacement for Ballack, who scored 14 league goals last season, and have experimented with several other midfielders off their talent-rich bench.
'With Ballack gone others will have to step in and take up the responsibility,' said Magath, who addded that Bayern are comfortable as favourites to win a 21st Bundesliga title.
Bayern lost 1-0 in a warm-up to Japan's Urawa Reds and then beat Schalke 04 4-1 on penalties in the League Cup semis before losing to Bremen, who could be their main challengers this term.
They were also beaten 3-0 by second division TSV 1860 Munich in a testimonial match for former striker Giovane Elber.
The match against Dortmund in Munich marks the return of single Friday night matches to the Bundesliga schedule.
Six matches, rather than seven, will be played on Saturdays at 1530 local time (1330 GMT) and two on Sundays at 1700 (1500 GMT).
Hamburg SV, who finished third last season and hope to challenge Bayern and Bremen for the title, host Arminia Bielefeld on Saturday while fourth-placed Schalke 04 host Eintracht Frankfurt.
Sunday sees an intriguing match-up when Bremen travel to Hanover just days after signing Germany defender Per Mertesacker on a four-year contract after a long struggle over terms with their northern German rivals.