The 21-year-old Frenchman signed a new three-year deal with Killie last summer but has quickly fallen out of favour with Johnston.
The former Le Havre striker - who joined the Ayrshire side in 2010 - has started just five games this term and made a further eight appearances from the bench.
His last outing saw him given a mere three minutes against Hearts two weeks ago and Gros admits his patience is wearing thin.
He said: “The last few weeks have just been the same as the rest of the year for me, sitting on the bench not playing much.
“I have a three-year contract but I don’t know what to do. Nobody wants to stay somewhere if they are not playing. We will see.
“I have a big decision to make. At the end of the season I will have to talk to the gaffer about what he is thinking and about what I’m thinking.
“If I were to play more I would be happy here at Killie. But it’s a professional pride thing. If you’re not playing you won’t be happy.
“I’m 22 at the end of the month so I need to be playing.”
Kilmarnock boss Johnstone has favoured Scotland striker Kris Boyd as the man to lead his attack.
With 18 goals you cannot fault the manager’s reasoning but Gros believes he could form an effective partnership with the ex-Rangers hitman given the chance.
“Boydy is scoring goals but I think we can play together,” said Gros. “But it is the gaffer who makes that decision. I just have to keep working hard and wait for my chance.”
Killie have just one win in their last seven games and sit just three points above second-bottom St Mirren as the battle to escape the relegation play-off spot heats up.
But Gros is eager to get involved in the survival fight when they visit new League Cup winners Aberdeen on Saturday and insisted he would not be affected by the tense situation at the bottom.
He said: “The pressure is always there but you just need to focus on what you are doing and perform.”