Barca lead Group B with nine points from three games heading into Tuesday's fixture in Milan, ahead of Inter (six points), Tottenham (one) and PSV Eindhoven (one).
Radja Nainggolan returns for hosts Inter, who are fresh from winning their seventh straight Serie A match on Saturday, after recovering from a left ankle injury picked up during last month's Milan derby.
"Leo is at the point where he might be available, but we have to wait for the training session. What we won't do is take any risks".
Barca have done well without Messi. His is the shirt that children who dream of being footballers ask for", said Spalletti, "but Barcelona have shown that even without him, they still have the mentality to develop their game, which is what makes the difference. "I never went to both clubs and said I want this player. We need to be better in our reading of the game, but we're going to mark space, not men".More news: Sheriff: 10-year-old says she stomped head of baby in panic
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Inter will seek hope in Barca's defensive record.
More crucially, key players have delivered while others, less prominent, have stepped up.
Coach Ernesto Valverde said on Friday he had not ruled Messi out of playing but was concerned about rushing him back.
"The fact that the team is doing well, in terms of performance and results, demonstrates that this is the chance to see if we really can compete against any side".