I completely agree with everyone who says that a 'gentleman's agreement' is worth nothing unless the terms are on a signed contract. However, in the real world, especially in industries driven by people rather than machines (think consulting/investment banking/R&D) there is an element of 'goodwill' shown by an employer to his employees, over and above any legal contract or law.
For example, in the consulting and banking industry it is very common for Principals (equivalent to really senior managers) to let their Associates or Senior Associates quit and join rival consultants/banks or even their clients without much fuss, many times even foregoing the full notice period. The thinking is that a person who is not motivated will not be an asset to the firm and the current consulting company/bank will have a contact (whose had a positive experience) in the rival firm/client for future business dealings.
Another example is Pharmaceutical R&D. Pharmaceuticals is a fairly small, niche industry where after decades of experience its hard to move to other industries. Hence Pharma companies regularly poach talent from each other, especially senior R&D management. In general, as long as the leaving R&D manager, does not take key members of his team, the current Pharma company will not make it hard for the manager to leave. The thinking is again that a person who is not motivated will not be an asset to the firm and the current Pharma company will have a contact (whose had a positive experience) in the rival firm for future R&D collaborations (such collabs happens a lot, especially in the last 20 years due to rising costs of developing a blockbuster drug).
Daniel Levy is essentially in a 'people-drive' business. 100 million at a time when the pandemic has raged for 2 years and continuing, is a fair amount for a top striker that's given Tottenham at least 3 years of his peak.
Don't agree with Kane missing training though.