A clutch player raises its performance.
Just a question for clarification. The original suggestion does not explicitly consider this sort of performance boost. It is only about choosing a preferred player for clutch plays. I understand this is not your interpretation or suggestion. So, is your suggestion to introduce an additional skill or trait for each player, or is it to simply give a boost for any player who is selected as a clutch player? I think both options are something that can be considered, but from the game play/design point of view they have different implications.
Let me explain what I mean and discuss the implications a little further. I will start with the latter, since it is the simple option. You select a player and he gets a (mostly scoring-related) skill boost for whatever plays the game engine considers a clutch play. Assuming this is already handled in some way in GE, the selected player is thus automatically more likely to take a shot (and score). This is potentially not a very difficult change to the GE. From the game play point of view, the choice is not necessarily a very challenging one but it should give some new variation in tactical choice. I have difficulty in seeing what is the real downside of the choice. It all seems strongly tied to your selected offensive tactic, which you can either enhance further or give a small safety net by making the clutch player decision. If you have a hero player who you can only make stronger, is the choice not obvious and thus not really interesting?
The other option is to give each player a new (hidden?) skill or ability to act as an effective clutch player. Thus, the manager sets his preferred clutch player and this player is given more weight in clutch plays. This is closer to how I understand the original suggestion, which has the disadvantage that the GE really needs some major work to make the suggestion in any way useful (based on what we know and can assume about the GE). This option however has one benefit over the original suggestion: the player now has a skill that directly affects the outcome. If it is a hidden skill, it would not even be as important to smartly rebalance the GE decision logic.
As I see it, the manager could override the "optimal" GE choices and force (or make significantly more likely) a certain decision, i.e. the decision to create the clutch player a scoring opportunity. By default, this is a suboptimal choice by the manager (it is important that you can make both a good and a bad decision). It also weakens your chances if you choose an otherwise good/hero player who is a weak clutch player. If the skill is shown, you will not make this decision (which suggests it should be a hidden skill). The obvious upside is that you can improve your chances, if you select a strong clutch player. I see that this would reward users who study their games and know their team. Thus, it is a fairly nice suggestion as such. I however think it needs some work in the GE. I don't mean this as critique of the suggestion, I mean it as a reality check.
There is an easy way to create a third option, which is to combine the other two. This would make it possible to have a "new player type" in the game: a role player who is a very strong clutch player. However, it would diminish the risk of selecting your hero player for clutch plays. It could also make the hero player with a good clutch ability too powerful. The third option would therefore need much more work, probably some balancing based on player skills or something.