PSG host relegation battling Le Havre on Saturday
Brazil forward Neymar hurt an ankle and had to be substituted early in the second half of Sunday's 5-0 win at Levante, while Croatia midfielder Rakitic has a bruised foot and both were having treatment.
How the injuries develop "will determine when they can return to training", Barca said on their website.
Barca are the only team to have won their opening four La Liga matches this season and top the standings on 12 points, two ahead of Sevilla.
After playing Malaga on Wednesday, Barca host Granada on Saturday before playing at Paris St Germain in the Champions League on Sept. 30.