Arsenal's Per Mertesacker says he is staggered by the revival at Werder Bremen, which has taken his former side from bottom of the Bundesliga to the verge of the European places.
Bremen were prime candidates for relegation in December before earning five straight wins and a draw to leap to eighth.
They host second-placed Wolfsburg on Sunday in a key clash with both teams unbeaten in 2015.
Mertesacker, who won the 2014 World Cup with Germany before retiring from international football, played for Bremen from 2006 until 2011.
He says he is delighted by Bremen's transformation under coach Viktor Skripnik and his assistant Torsten Frings, Mertesacker's former Werder and Germany team-mate, who took over after Robin Dutt was sacked in October.
"I am such good friends with (Bremen captain) Clemens Fritz that I hear of any problems first hand," Mertesacker told Sky Sports.
"And then they win five games in a row. It is simply crazy how the new coaching staff has turned things around.
"And that is with a team who previously had taken four points from 10 games."
Bremen's fortunes have been helped by ex-Chelsea and Wigan Athletic striker Franco di Santo, who has scored four goals in as many games in 2015.
Sunday's clash at Werder's Weserstadion pits the league's two form teams against each other with Wolves led by striker Bas Dost, scorer of nine goals in his last five games.
Consecutive wins over Borussia Dortmund, Hertha Berlin, Hoffenheim, Bayer Leverkusen and Augsburg, followed by a draw at Schalke 04, have left Bremen just outside the European places.
But Mertesacker says Bremen's dramatic revival is unusual in modern football.
"Things happen so fast in this day and age," said the 30-year-old.
"On one hand, it's bitter that the coach can be sacked so fast when things go wrong, but on the other hand it's nice to see things work again so quickly."
Mertesacker has been brought back to earth with Arsenal this season after the highs of winning the World Cup in Brazil last July.
The Gunners were beaten 3-1 on Wednesday at home by Monaco in their Champions League last 16, first-leg clash, and face an uphill task to progress.
"We overdid it, we wanted it too much and made several wrong decisions, that hurts," he said, adding Arsenal have only "a tiny hope" for the away leg on March 17.