The 34-year-old has yet to come face-to-face with his former employers since leaving the Red Devils for Real Madrid in 2003, and is not assured a starting place in the Champions League last 16 first-leg having been benched in recent weeks.
The ex-England captain - who made more than 350 appearances for United - has vowed not to celebrate should he find the back of the net against Sir Alex Ferguson's side.
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However, Seedorf believes that Beckham has every right to enjoy the moment.
"Should Beckham score, he must celebrate his goal. It has nothing to do with respect," he said in The Sun.
"Scoring in a match of this calibre is something extraordinary. He will be very emotional, but am sure that he will do well."
The veteran Dutch midfielder added that, in his eyes, holders Barcelona and Premier League leaders Chelsea - eliminated by an injury-time goal from Barca in last season's semi-final - remain the teams to beat in 2010.
"Neither [Milan or United] are amongst the favourites to win the Champions League. We are considered as being outsiders.
"The English side are going through a transition period caused by the sale of Cristiano Ronaldo.
"We are in the same boat, having lost Kaka and [Paolo] Maldini and arriving in their place new players and a new coach.
"Barcelona and Chelsea are in pole position to win."
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