Gloucester ground out a 27-13 victory over a winless Bucuresti to ensure quarter-final qualification, and Ryan paid tribute to the home side.
"I thought Bucuresti played outstandingly well and that is a great credit to them," he said.
"From our point of view, there was a quality issue but I thought we adapted well and got the four tries and the bonus point.
"It was a difficult environment but we came here and got a job done and that's the most important thing."
After Gloucester's 106-3 mauling of the Romanians in the first-leg match at Kingsholm, visiting fans were left scratching their heads as their side led only 5-0 at half-time.
South African back-rower Jake Boer was the only man to trouble the scorers in the first spell, scoring his fifth try in three European matches.
Gloucester moved up a gear in the second half with tries to hooker Rob Elloway and replacement scrum-half Peter Richards, before a late penalty try ensured a bonus point.
The Cherry and Whites are guaranteed a Cup quarter-final, with next weekend's final Pool 3 match against Bayonne at Kingsholm deciding who tops the pool and secures home advantage in the play-offs.
Northampton moved ahead of Bristol in Pool 1 with a 45-8 win over their English rivals in front of a Challenge Cup-record crowd of 12,227 at Franklin's Gardens.
New Zealanders were to the fore, with back-rower Sam Harding scoring a try double in the opening 10 minutes to propel the Saints to a comfortable victory ahead of next weekend's final match against Viadana in Italy.
Another New Zealander, fly-half Carlos Spencer, added a first-half try as the Saints took a 19-3 lead into half-time, and a third Kiwi, scrum-half Mark Robinson, sealed a bonus point.
England winger Ben Cohen scored his side's fifth and sixth tries, and New Zealand fullback Bruce Reihana added 10 points with the boot.
Lock Mariano Sambucetti scored a last-minute consolation for the visitors.
London Irish sneaked home 19-11 against Rugby Parma in Italy, and can secure a valuable home quarter-final with a win over Pau next weekend.
Outside-half Ross Laidlaw capped a fine game with a first-half try, before back-rowers Phil Murphy and Declan Danaher scored to seal the victory at Stade Sergio Lanfranchi.
Worcester retained the top spot in Pool 5 with a comfortable 44-8 win over Amatori Catania at Sixways Stadium.
The home side eased to a 25-0 lead on the back of tries to centre Dale Rasmussen and back-rowers Johnny Tuamoheloa and Drew Hickey, and bagged a try bonus point in the opening exchanges of the second half.
Catania stemmed the flow midway through the second spell before conceding a last-minute try to former England scrum-half Andy Gomarsall.
In Galway, Connacht kept the pressure on Worcester in Pool 5 with an impressive 43-10 win over Montpellier.
The home side led only 7-3 at the break, but moved up several gears in the second spell to run away with the match. Back-rower Matthew Lacey and centre Keith Matthews helped themselves to try doubles to secure a valuable victory.
In Pool 4, Brive hammered L'Aquila 47-19 in Italy.
Pool 4 leaders Newcastle Falcons play Border Reivers on Sunday.
On Friday night, Bayonne kept the pressure on Gloucester in Pool 3 with a 62-0 mauling of fellow French club Touloun. Bayonne ran in 10 tries, including three to winger Benjamin Lhande.