Messi guided Barcelona into the quarter-finals with a star display in the second leg of their last-16 tie with Chelsea on Wednesday.
After his goal in the 1-1 first-leg draw at Stamford Bridge, the Argentine put the ball through the legs of Thibaut Courtois to open the scoring early on in Camp Nou before setting up Ousmane Dembele after an impressive run. Messi netted another in the second half, capitalising on the space between Courtois' legs once again to take his career tally in the competition up to 100.
Ernesto Valverde's men avoided the likes of Manchester City, Real Madrid and Bayern Munich in the last four when they were paired with Roma, but Shevchenko feels it does not matter who Barca come up against in the competition as long as Messi remains as decisive as he was in midweek.
"If Messi plays like that, as he did on Wednesday, Barca will be European champions this season," the former Ukraine international told Mundo Deportivo.
"This Messi is unstoppable. We already saw it against Chelsea. He's at a very high level."
Asked who he would back to go on and win it if Messi fails to replicate his heroics, Shevchenko said Real Madrid or Man City appear the next favourites.
Messi and Barca welcome Roma to Camp Nou for the first leg of their tie on April 4 before the return fixture on April 10.