Sir Alex Ferguson believes a master pupil from his past could make life difficult for United tonight (Tuesday).
Birmingham City boss Alex McLeish served under the Reds supremo during Aberdeen's glory days and showed signs then, as a player, of one day following his namesake into management.
"Alex McLeish is without doubt a formidable manager," Sir Alex told MUTV.
"He's a very intelligent lad. I knew, even when he was a kid at Aberdeen, that he was going to be a manager. He had a real interest in the game, he was always reading football magazines or asking questions about the tactics or the training. He was always devouring knowledge so I'm not surprised he's done well down there."
Sir Alex acknowledges that McLeish has made Birmingham "very difficult to beat", certainly at St Andrew's where they boast "a terrific home record." The Blues have lost only one of their eight league games there this season - to Everton in early October - and the teams they've sent home empty-handed include Chelsea.
United, meanwhile, must improve on the last meeting - January's 1-1 draw at Birmingham - if the Reds are to claim only a second league away win of 2010/11, the first since Stoke on 24 October.