But boss Ernesto Valverde insists he will not "risk" the Argentinian genius, who is targeting a return from his broken arm.
Valverde will pick a strong XI as his team look to win the group and book a spot in the Champions League knockout stage by beating Inter.
Messi was named in Barca's preliminary squad on Sunday for the clash – despite breaking his arm just over two weeks ago.
He took part on training on Monday night and is expected to be given the green light to play by medics.
But reports in Spain say Messi is likely to start the San Siro game as a substitute.
Before last night's training session, Valverde said: "I have many options. I cannot anticipate anything because we have not trained yet, but I am sure that we will not take any risks.
"I think it's better that he's in. I have the feeling that we'll go with him, but of course he needs to recover as soon as possible.
"Leo is at that point where he can be available, we'll see what he feels, he has to have that security point to play."
Messi broke his arm against Sevilla on October 20 but has returned to training a week sooner than expected.
He has 12 goals in 12 games for his club this season and Barca are three points clear of city rivals Espanyol at the top of La Liga.
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