Rangers, now sure of a play-off place, trailed to Mathias' Ranegie's goal six minutes into the second half before Joey Barton's 76th-minute free-kick hauled them level.
Top scorer Austin, badly missed during a recent two-month spell out with a shoulder injury, gloriously curled home his 16th goal of the season in the closing stages.
But he was immediately substituted after the goal celebrations and appeared to have hurt his hamstring.
However, Bond said: "It was probably more from fatigue. He was just that shattered - he was all out.
"Hopefully he is okay and I think he is. We obviously need to assess him and I haven't got round to speaking to him yet. We'll need an update, perhaps tomorrow."
Watford's defeat means their play-off chances look remote, and they can consider themselves unfortunate, having dominated large spells of the match.
Bond added: "I was impressed with Watford. They started both halves better than we did but we eventually got hold of the ball.
"It was great for Charlie to get back on the scoresheet. We've missed his goals and missed his presence.
"Apart from what he does on the field, psychologically when the teamsheet goes up and he's not been on it, no disrespect to anyone else, but we know he has won us games.
"It was a great finish under severe pressure and he kept his composure really well.
"We now need everybody fit and in good form for the play-offs. We need to get the momentum."
Watford boss Sannino described his team's display as their best since he took over in December.
The Italian said: "It was a very important game for us, almost a must-win game, and we were knocked down when we tried to score from a corner.
"They counter-attacked very well and we conceded in a game in which I think we produced the best performance under my regime.
"Of course with a draw we would have one more point, but my lads deserved more than one point. For 60 minutes there was only one team in the game.
"Maybe I became too British. I like your culture and will to win until the last second of the game and if I'd kept three defenders back at that corner we might not have conceded the goal.
"But I don't have regrets, because that's the way I like to be and I'm pleased with my lads because we tried to score.
"I'm happy because my team played well, but on the other side there is a bitter taste because of the result."