The Spain goalkeeper is set to leave the club at the end of the season, and if the injury to his right knee - sustained while making a simple save - proves serious, he may have played his last game in a Barcelona shirt.
There was a further worry for coach Gerardo Martino when Andres Iniesta was withdrawn at half-time as a precaution with a niggling thigh problem.
Yet, three days after Sunday's epic Clasico victory, a routine win at Camp Nou at least allowed Barca to apply further pressure to La Liga title rivals Atletico and Real Madrid.
The visitors threatened sporadically, most notably just after half-time when Valdes' replacement Jose Pinto made an excellent double save to deny Augusto Fernandez and Santi Mina.
Celta were already two down by that stage, however, Neymar having finished off a trademark flowing move from Barca with a simple tap-in, before Messi ran on to Iniesta's pass and beat goalkeeper Yoel for his 22nd league goal of the season.
Neymar, who had come in for criticism following his performance against Real, added his second and Barcelona's third in the 67th minute, allowing the Catalan giants to celebrate their 1,000th La Liga match at Camp Nou in style.
The Brazilian's opener came inside six minutes as he tapped into an empty net after incisive approach play involving Iniesta, Messi and Alexis Sanchez.
Despite a lengthy stoppage, Barca's rhythm was not disrupted as Messi doubled the advantage on the half-hour, latching on to Iniesta's pinpoint pass before rounding Yoel and slotting in.
Seven minutes into the second half, Pinto made a superb double stop, first keeping out Fernandez's close-range prod before jumping to his feet to parry away Mina's powerful rebound.
Neymar then put the result beyond doubt, picking up Sanchez's raking pass before firing beyond Yoel low into the bottom right-hand corner.
