Leicester boss Richard Cockerill believes it is "unrealistic" for Manu Tuilagi to be part of England's early games in the RBS 6 Nations Championship this season.
England and Tigers centre Tuilagi made a long-awaited comeback from injury as Leicester claimed a dramatic last-kick 30-27 victory over their fierce Aviva Premiership rivals Northampton at Welford Road.
New England head coach Eddie Jones looked on as Tuilagi, who had been sidelined for 15 months due to a serious groin problem, made a 52nd-minute substitute's appearance.
Tuilagi was a late inclusion on the Leicester bench - his appearance in the match-day 23 was announced less than an hour before kick-off - and he must now wait to see if he makes Jones' first elite player squad, which will be unveiled next Wednesday, 24 days before England's Six Nations opener against Scotland at Murrayfield.
Cockerill, though, has urged caution about any prospect of Tuilagi being rushed back into the Test arena.
"I am not sure how far off full fitness he is in 80-minute terms," Cockerill said.
"He played 25 or so minutes today, and he is remembering how to play rugby again. Hopefully, there will be no reaction to that.
"He will play next week, and we will build his fitness up gradually. At this point, I am not sure he is ready to play Test match rugby.
"He has played 25 minutes in 15 months, and it is a bit premature to be discussing Manu playing for England.
"He needs to play for Leicester, we need to get him fit and make sure he is 100 per cent right before he starts playing Test matches.
"I will speak to Eddie in the next few days. Manu will keep improving, but the start of the Six Nations is unrealistic because we need to make sure he is 100 per cent right."
Saints hooker Dylan Hartley missed the Leicester game due to a rib injury, although Northampton rugby director Jim Mallinder suggested it is not a long-term problem.
"He got a bang to his ribs last week," Mallinder said of Hartley, who had been due to be on Saints' bench against Leicester and has been touted as a possible England captaincy successor to World Cup leader Chris Robshaw.
"He trained a little bit in the week but at the last minute, he was just too sore to play today.
"We were hoping that he would come through and be fine. It's a bang to the ribs, and he has done some training this week, so he is not going to be out for a long time.
"But I guess ribs are one of those things, and particularly when you are scrummaging, you are not exactly sure how it is going to affect."
The Tigers stormed 21-0 ahead through converted tries from centre Matt Smith, number eight Lachlan McCaffrey and fly-half Owen Williams, who finished with 11 points before departing nursing a suspected broken jaw.
Saints cut the gap to four points through tries by Teimana Harrison and George North and seven points from JJ Hanrahan before two second-half penalties by Freddie Burns appeared to seal the deal for Leicester.
But former Tigers flanker Jamie Gibson scored a third Saints try and Stephen Myler's penalty looked to have completed a stirring fightback before Burns' last-kick clincher.
Cockerill added: "Credit to them for getting back into it, but credit to our players for the first 30 minutes and then for digging themselves out of a hole they probably shouldn't have got themselves into.
"Good sides win when they do some average things, and we did some average things today but we found a way to win, however fortuitous that may or may not have been."
Saints saw a second-half try for prop Paul Hill disallowed when referee Wayne Barnes penalised Saints centre Luther Burrell and replacement Tom Wood for a high tackle, while Burns' last-gasp winner came after Courtney Lawes was penalised.
"My reaction is clearly one of disappointment," Mallinder said. "I spoke to Courtney afterwards, and he said he tripped.
"In the first half, we had a terrible 20 minutes - they were good, but we were terrible for 20 minutes - and you should not go 21-0 down at Welford Road.
"But we came back into it. We really got some good momentum in the second half and that (high tackle penalty) was a massive moment, because I am pretty sure if that (try) had been allowed then I think we would have gone on and won the game."