Arsenal appear on the verge of bringing in veteran goalkeeper Petr Cech from Chelsea.
Manager Arsene Wenger is also expected to strengthen the outfield, with targets such as Porto forward Jackson Martinez, Monaco midfielder Geoffrey Kondogbia, Borussia Dortmund's Sven Bender and Southampton's Morgan Schneiderlin
It is, however, the performances of Sanchez, now leading Chile's hopes at the Copa America, which for Henry will be key.
"As an Arsenal fan I am very excited about next season and hopefully we can bring some people to the club, some new players maybe but when you have a guy like Alexis Sanchez anything can happen
Hopefully he can fire us to the title next year," said Henry, Arsenal's record goalscorer and member of the Invincibles 2003/2004 squad.
"Look at what he did in the FA Cup final and what he has been doing since his arrival
He has been more than tremendous."
Henry said on Arsenal Player: "We want to see that more and more and I know that he has that in his locker
When you have a guy like Alexis Sanchez, it is the X-factor
"He is the guy who can change the course of a game
I love the way he plays, he plays with his heart and I know the fans love that about him."
The departure of Arsenal goalkeeping coach Tony Roberts for Swansea has fuelled speculation the way is being cleared for Cech's arrival from Chelsea.
The 33-year-old hopes to stay in London, and despite Blues manager Jose Mourinho not wanting to sell him to a direct rival, is believed to now have accepted the wishes of the player who does not want to remain as understudy for Thibaut Courtois.
It has been suggested Chelsea goalkeeping coach Christophe Lollichon would also be making a switch to the Emirates Stadium.
Should Cech's expected arrival materialise, then David Ospina could be set to depart just a season after the Colombia international's arrival from Nice, with Fenerbahce said to be a likely destination.
Source : PA