Sir Alex Ferguson came up against the new interim Manchester United boss Ralf Rangnick during his own time in charge of the Red Devils, in a Champions League clash with Schalke.
Rangnick was in charge of the German side for a season and faced off against Man United over two legs in the semi-final of the Champions League back in 2011.
Ferguson and United came out on top in the contest, winning the first leg 2-0 before thumping Schalke 4-1 in the return fixture to record an impressive 6-1 aggregate scoreline.
But Ferguson was clearly wary of what Rangnick was capable of ahead of the game, and was impressed that the German's Schalke side were in "complete control" against Inter Milan in the quarters.
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Ferguson said in 2011, ahead of the semi-final: "They [Schalke] have beaten every team they have played in the Champions League at home this season, including Valencia and Inter Milan.
"Taken in isolation, that's fantastic form and there is no way Manchester United are going to be led into believing that this is easy. This is a difficult game for us and we have no choice but to treat it that way."
He added: "They never looked like losing the game and that's quite a credit to them in terms of playing a side like Inter Milan.
"They always looked in complete control and, even in the good spells that Inter had, they [Schalke] never looked like losing. It's a semi-final now and, any semi‑final you go into, you know it is going to be difficult."
Rangnick was equally respectful of Ferguson, saying of the Scot: "He is the complete boss.
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"You can only take your hat off to the 30 years he has coached and reigned over that club. The fact he still feels that fire and desire to lead the team to titles is extraordinary."
Rangnick was recently named interim United boss and will command control until the end of the season.
The German will then move upstairs where he will work a consultancy role for at least two more years and will have a say on who replaces him in the hot seat come the end of the campaign.
