Smalling and Jones are recovering from injuries that occurred during a training ground incident while preparing for England's match against Germany in March. 24-year old Pogba returns after copping a knock against Burnley on the 23rd of April.
"Smalling, Jones and Pogba are back and, in relation to the Europa League, it's very important," said Mourinho.
"They came on time. We have two important matches in one week against Celta. It's important to have everybody back."