The French striker pulled up in the first half of the European champions' 2-0 La Liga win at Malaga and was replaced by Zlatan Ibrahimovic.
Henry's absence adds to Barca's problems up front for the Group F clash against the Ukrainians, with teenage forward Bojan Krkic sidelined and Sweden striker Ibrahimovic still recovering from a minor sprained ankle.
"Andres is still not quite at 100 percent and needs a bit more time," Guardiola said.
"The reason we haven't used him more is because we are taking it step by step," he added "But he is much better and we will be using him more and more as time goes by."
Barca's Ukrainian defender Dmytro Chygrynskiy, who moved from Shakhtar Donetsk in the close season, is unable to play for the Catalans in the Champions League as Shakhtar used him in the qualifying rounds.
"You have to remember they are the Ukrainian champions," Chygrynskiy told Barca's website.
"Their style of play is to pressure their opponent and deny them space," he added. "They are very strong physically and very quick on the counter."
"But he's in good form and tomorrow he'll be in the starting lineup," Gazzaev said.
"Shevchenko is an extraordinary player and one of the best ever in the Champions League," he added. "It'll be interesting to see what we are capable of tomorrow."
