Messi returns for PSG after Saudi trip ban
The 35-year-old World Cup winner was banned by the club after an unauthorised trip to Saudi Arabia.
"Yes, Leo is going to start tomorrow," Galtier told an eve of match press conference.
"Obviously I've spoken to him, he's very relaxed, really keen to play, and very determined to claim another French league title."
With PSG out of the Champions League and only four Ligue 1 matches remaining as they target a record 11th title, this is likely to be Messi's penultimate appearance at the Parc des Princes.
After an uninspiring two years in France, the seven-time Ballon d'Or winner is reported to be lining up a blockbuster deal to play in Saudi Arabia next season where he would join his old sparring partner Cristiano Ronaldo.
His move to Saudi or even his departure at the end of his contract in June, however, have yet to be confirmed by the club or his agent father Jorge.
But all the signs are that he is on his way out.
"Messi is a done deal. He will play in Saudi Arabia next season," a source close the negotiations speaking on condition of anonymity told AFP this week.
Galtier said he did not want to go into the six-day suspension which forced Messi to miss last weekend's 3-1 win over Troyes that left PSG six points clear of Lens.