Spurs must overturn a 1-0 Champions League semi-final deficit in Amsterdam to reach the final.
“We have proven it a lot of times this season," said Frenchman Sissoko.
“We've had plenty of injuries but we still won some games and we still played some good games. That means we have a strong team and a lot of character. So if someone is injured, someone else can play and succeed as well. That's good for us. That's why we are a good team.
“We fight all together, we fight for each other and that's the only way you can improve. That's why we are here right now. It's because we give everything together and thats what we will try to do again at Ajax for the second leg."