No I am not a doctor and no I do not know more than the Celtics medical staff. I will include links to studies on this for anyone who wants to read before complaining.
It is well documented that when returning from Achilles tears, athletes tend to over compensate with the non repaired leg, leading to injury. Kobe Bryant tore his knee in the opposite leg just 5 games after returning from his 9.5 month recovery.
Tatum has been logging 40 playoff minutes a night not even a year after surgery. It is not a shocker that complications in his other leg are starting to show.
With Achilles tears rising in the nba, every player who has torn it recently, including Tatum, has said they felt discomfort in that calf before the injury. Obviously it is unlikely any major injury would happen if he plays, but it is absolutely not worth the risk. This team has no chance of winning the title this year anyways, just shut him down and retool for next year.
https://pubmed.ncbi.nlm.nih.gov/14723785/