The Jags head into the Irn-Bru First Division fixture on the back of a 2-2 draw with title rivals Morton that leaves them eight points off the pace in the Irn-Bru First Division promotion race.
Alan Archibald's side play the first of their three games in hand over the Ton this evening as they host Accies, with fixtures at Cowdenbeath and Raith Rovers also to come as they set their sights on top spot in the standings.
Thistle's title destiny is still in their own hands and O'Donnell is ready for a gruelling period that could make or break their SPL dreams.
He said: "I don't know if I would go as far to say that it is a must win. The point on Saturday means that it is still in our hands, which is good.
"I would rather it was still in our hands as now but, at the same time, points on the board are important. We need to take each game as it comes and hopefully we can get the three points against Hamilton and move on.
"It is a good time for Archie to have a full squad, it is one of the few times this season where everyone has been fit. We all feel we are good enough to play and it is disappointing not to play.
"But, it is a team game and we will be called upon at some point whether it is next week or in the weeks to come."
The Firhill fixture tonight will see Archibald take charge of the Jags for the first time on home soil following the departure of Jackie McNamara.
It could also herald a return to the starting line-up for O'Donnell after his recent injury lay-off saw him out of action for several weeks.
He made a late Cappielow cameo on Saturday, replacing Steven Craig just seconds after Hugh Murray added another red card to Thistle's mounting tally this term and the right-back is eager to play his part.
He said: "It was nice to be back involved again, although it was in disappointing circumstances with Shug going off.
"I was glad to get a run-out and hopefully it increases my chances of getting a game against Hamilton tonight.
"I did think Archie might tell me to sit back down again but I was glad to get on and play. It is never easy when you are down to 10 men but we did well to defend and to get the point.
"It was disappointing to lose the two goals after being 2-0 up but I think it was a good point for us.
"You just need to get on with it. Hopefully come the end of the season it won't affect where we finish."
Meanwhile, Thistle face a midfield shortage for their trip to Dunfermline next month with Murray and Paul Paton set to miss the East End Park clash on March 2.
The fixture will be the second match of Murray's suspension following his dismissal on Saturday while Paton has been ruled out after being booked at Cappielow, his sixth caution of the league campaign.