Jones picked up a toe injury and fellow centre-back Smalling was pictured with a leg brace following an injury also suffered in training.
Asked how long he expects to be without Jones and Smalling, the United boss said: "I don't know, I don't know.
"I know that Zlatan and Herrera have the last match ban, so it's easy to say they will be available after the match.
"I think clearly the two English boys they are long-term injuries and Pogba I have no idea. I don't know."