There's no need to panic at this point. Gausman himself expects to be ready to start the regular season as scheduled. If he misses time the team actually has plenty of depth to weather a short term absence. Manoah provided essentially no value out of the rotation last season so even the team's the least desirable depth options like Parsons could actually be more effective rotation options in his absence.
If the team has a rough April it's not the end of the world in a 6 month season. They had an awful May last season and still qualified for the post season, a single rough month in not something to panic about.