The Chelsea boss is prepared to run the rule over those in his squad who spent the last campaign away from Stamford Bridge, including midfielder Michael Essien, who played for Mourinho at Real Madrid.
Striker Romelu Lukaku scored 17 goals for West Brom last season, while playmaker Kevin De Bruyne had been linked with Bayer Leverkusen after an impressive spell with Werder Bremen in the Bundesliga.
Lukaku and De Bruyne seem likely to be given a chance to impress for the Blues by the returning manager, who is keen to take a look at all the players at his disposal once his squad reconvenes.
"I need to work with the players and not commit injustice," Mourinho said.
"I need to give them a chance, be fair with them. After that we will have time to make decisions."
Chelsea's pre-season includes a game apiece in Thailand, Indonesia and Malaysia, as well as a meeting with Mourinho's former club Inter Milan in Indianapolis, USA.