The Blues midfielder has been nursing niggling knocks throughout pre-season, preventing him from building the kind of fitness levels he would like heading into a new campaign.
There is, however, still time for Lampard to put himself in contention for a starting berth against Hull City next Sunday.
He came through 45 minutes against Real Madrid in Miami and is being lined up for a more extended run-out in a meeting with Roma on Sunday.
Mourinho said of Lampard, who has been named in the latest England squad: "Frank's not ready yet, he still has to train. He has to play against Roma on Sunday. He played 45 minutes against Real, maybe he plays 60 minutes against Roma.
"He's in the England squad, so it will be good if he plays against Scotland."
While Lampard is being eased back into action, Mourinho will not be taking any risks on David Luiz and Juan Mata ahead of the 2013/14 campaign.
He added: "They are important. The team with Luiz and Mata is a better team.
"But again we don't risk players in pre-season. Mata had a little injury so we didn't take a risk. David had a hamstring injury so we said 'stop'.
"I'm not risking him here so, hopefully, there's no problem for the start of the season."