Each had been in NHL COVID-19 protocol.
Grubauer, a goalie, and Donskoi, a forward, each missed five games after testing positive. Rantanen, a forward, missed four games because of contact tracing.
"I don't know how those guys are going to be after their break," Colorado coach Jared Bednar said Friday. "It's not easy to come back in and pick up where you left off, but those guys have been putting in some good work. You get your starter back in net, you get some scoring back in the lineup, you become a more confident team and you can cover up for some of the mistakes you make."
Grubauer was placed in protocol April 14 and was expected to be out at least two weeks. He was removed from protocol April 23 and returned to skating Tuesday.
Grubauer is 25-8-1 in 34 games with a 2.00 goals-against average, .920 save percentage and five shutouts. He was tied for the NHL lead in wins with Andrei Vasilevskiy of the Tampa Bay Lightning; Grubauer now trails Vasilevskiy by five.
Donskoi, who was placed in protocol April 16, was removed Monday and returned to the ice Thursday. He scored 28 points (15 goals, 13 assists) in 42 games.
"I had some symptoms and it [stinks]," Donskoi said. "I'm happy it's over now. It was a tough couple weeks for sure. I skated for the first time yesterday, trying to get back at it, to get my skating back and all that. I'm good to go, so it's good to jump back in and playing games, there's no better way getting back."
Rantanen, who had been in protocol since April 20, was removed Monday and skated Tuesday. He scored 52 points (26 goals, 26 assists) in 43 games, second on the Avalanche behind center Nathan MacKinnon (61 points; 19 goals, 42 assists in 43 games).
Colorado, which had three games postponed from April 16-20 because of COVID-19 protocols, had lost three straight games after going 18-1-2 in its previous 21.
"Of course you want to be out there as much as you can," Rantanen said. "Watching those games was tough, you always want to be a part of it. I'm happy to be back now and I'm feeling pretty good. I've been skating for a few days, so that helps. I feel pretty good actually right now. It comes back quick. Obviously I'm ready to play big minutes and just try to play my best to get the win. Not too many expectations for myself, just for the team."
The Avalanche (31-12-4), who have clinched a berth in the Stanley Cup Playoffs, were second in the Honda West Division, six points behind the Vegas Golden Knights.
