Let's say I have a bull call spread and I get assigned. The option is american style and physically settled. Do I physically need the money to purchase the underlying at the bought call strike? For example, Let's say SPY is at $98 and I buy a call contract at strike $100, and sell a call contract at strike $101 (same exp). The spread costs me $50 (or .50 per share). Now, SPY goes to $102 and I get an early assignment. Do I physically need 10k to exercise my purchased call? Or can I somehow simultaneously exercise my bought call and sell the shares to the sold call and net the $50? The difference is, if I physically need 10k, then my yield is .5%. If I don't need 10k, then my yield is 100%.
If you are assigned on a short call you get a short stock position in your account, and if you then exercise your long call then you would be covering the short position so you don't need the money to purchase the shares. However, I suggest you check with your broker so you don't get a nasty surprise.