I'd begin by trying to understand why they're asking to skip discovery?
Your approach is going to deeply depend on what their underlying motives and/or fears are.
For example, I've been in this situation and the answer that I unearthed was that they had a KPI to ship a product by x date, their motive was not to ship something good but to hit their KPI. As a result I could then navigate this by still helping them achieve their KPI but whilst finding spaces where we could do discovery.
Other times I've either been in this situation or the PMs I've coached have been I've unearthed fears like "worried that discovery will be long and costly", "don't see the value in it", etc.
Depending on what the motives/fears are, you can then help address them accordingly:
If they don't see the value in it then that's often a simple one = education. But sometimes it's not that straight forward as it's hard to imagine something you haven't experienced yourself. So rather in these situations I look to see if we can get agreement on a short discovery, say a 5 day design sprint or 2-week discovery. I would then involve that leader in that discovery as much as possible, bring them to customer interviews, ideation, etc make them experience the value for themselves.
Another common scenario is discovery being viewed as timely and costly. First, I've it's good practice to always timebox discovery but it can also help with these situations. If you can create buy-in that you will only do discovery for x days or weeks that'll help alleviate this concern. More often than not they're envisioning 6-8 weeks of discovery and when you say we're going to timebox for 2-4 weeks, crisis adverted.
A tool I have regularly used in these situations to help facilitate this conversation is this one below by Jeff Patton:
Along the y-axis is how confident or "how much would you bet?" on this opportunity and along the x-axis is how much discovery you should ideally invest.
Using this matrix I've left of the middle and then asked stakeholders pushing for (less or) no discovery to put how much they're willing to bet on the opportunity. If they mark the top of the y-axis then all good, let's skip discovery however if not then there's a conversation about avoiding the 'stupid zone' and why we should invest 3 days or 4 weeks (whatever it lands on) into discovery.
Although the tool has the sweet spot the idea is to really help facilitate the conversation. Depending on how much risk you're willing to take you might step outside of the 'safe zone' but the idea is to do so deliberately.