"It's hard enough to work on the rehabilitation and for him I don't know if he's going to find the motivation to want to still play," Seedorf, the only player to win the Champions League with three clubs, said in an interview on BBC Five Live.
"Let's just see. The most important thing is for him to get fit," added the 33-year-old former Dutch international.
"For a couple of weeks he will need psychologically to get back in the right shape to face the coming months working on his injury."
The 34-year-old Beckham, on loan at Milan from Major League Soccer side LA Galaxy in a bid to earn a spot in Fabio Capello's England squad for this year's World Cup in South Africa, had surgery on his Achilles in Finland on Monday.
Surgeon Sakari Orava said the operation had gone smoothly but that there was no chance of Beckham recovering in time to play at his fourth World Cup after suffering the injury in Sunday's 1-0 Serie A victory over Chievo.
Seedorf, who scored the winner against Chievo, said he sympathised with Beckham, England's most capped outfield player with 115 caps.
"It was quite a shock knowing what happened when I got in the dressing room," he said.
"I went directly to him and spent some time with him but he was really in a lot of pain ... you could see his whole picture just flying away, his dream of being in the World Cup, all his efforts to come back to Europe.
"It was quite a sad moment and I felt for him but he is a strong guy and I'm sure he will look at the bright side even if there isn't much of a bright side right now for him.
"I could see his face was full of pain but it was not just that, it was all the other things fading away in front of your eyes, the World Cup had gone away."
NEWS:Surgeon - Beckham operation successful
