The England international could be a doubt for the upcoming friendly with Scotland after it was confirmed he will only play a small role in his club's pre-season tour of the USA.
Lampard did not feature in Chelsea's Asia leg of their pre-season and missed the opening game in America against Inter Milan on Thursday night.
Mourinho has now said the midfielder will also be absent versus AC Milan on Sunday and will only feature in possibly the next friendly versus either Everton or Real Madrid, or the following tie with Roma.
Mourinho said in the Daily Star: "Frank is recovering but of course we don't want to take risks.
"Hopefully he plays - I won't say the second match but maybe the third or fourth."