The French striker, who was second choice at the start of the season as Arsene Wenger chose to play Alexis Sanchez in the number nine role, has played himself into contention scoring five goals in his last seven starts for the Gunners.
According to the Times, Giroud picked up a minor ankle injury during the clash against the Hornets, which was the reason he was replaced by Theo Walcott during the interval. Alex Oxlade-Chamberlain, meanwhile, is expected to be fit despite Wenger confirming a kick to the knee during the game.
The France international's short-term absence will not be a cause for concern for the manager as he has a number of options available in attack at the moment. Danny Welbeck has returned to the fold and impressed during his first start in the FA Cup against Southampton, while Lucas Perez will also be itching for a start in the Premier League after impressing during his 16 appearances in all competitions thus far this season.
Arsenal are facing a season defining game at the weekend against the league leaders at Stamford Bridge and Wenger has changed approach in terms of preparation. The French coach has reportedly given the team two days off from training and will have just one session prior to their game against the Blues.
The Gunners' title challenge will be over if they lose on Saturday, and the main challenge facing the manager is a lack of midfield players at the moment. Aaron Ramsey is certain to miss the clash against Chelsea after picking up a calf strain against Watford, while Granit Xhaka and Mohammed Elneny are unavailable due to suspension and international commitments respectively. Francis Coquelin is the only fit midfielder available, which could see Wenger again deploy Oxlade-Chamberlain in a deep lying midfielder role like he did against Southampton on Saturday (28 January).
Arsenal are hoping that the Welsh international will be available sooner rather than later, as he came off as soon as he felt his calf tightening, and is said to be confident that he has not torn a muscle. The north London club have crucial clashes against Liverpool and a two-leg Champions League clash against Bayern Munich in coming weeks and will hope to have Ramsey's services for their trips to Germany and Anfield.