McCoist handed the former Aberdeen man his first start in nearly two months at the weekend in the SPFL League One meeting with Stenhousemuir at Ochilview.
And the right-back, who had been sidelined with ankle ligament damage, grasped the opportunity he was given firmly with both hands.
His pinpoint cross to the edge of the opposition box set up Nicky Law for the opening goal of the game in the first half.
And after Arnold Peralta had been red carded, the defender helped ensure the Ibrox club kept a clean sheet in their third away game in six days.
The 28-year-old had been a regular first team starter before sustaining his injury in a bruising encounter against Dunfermline at the start of November. But since regaining full fitness last month he has been kept out of the starting line-up by his replacement Sebastien Faure.
It has been hard to argue with Faure's continued involvement as the former France Under-20 international has been consistent.
Foster, though, is hopeful his bright personal performance in the 2-0 win on Sunday has now given his gaffer a serious quandary.
"Like any other professional footballer, I want to play as many games as you can," he said.
"I suppose I was lucky that Bilel (Mohsni) got suspended in the game against Airdrie and created an opening in the side. I got a break there.
"The manager moved Seb across to centre-half and put me back in at right-back.
"Hopefully I have repaid his confidence with a good display. A clean sheet was pleasing and obviously we won the game."
Foster added: "There is fierce competition for places at Rangers. We have a big squad and a good quality squad as well.
"So nobody is guaranteed a place in the team. There are three or four players here who can play at right-back and play there well.
"Whoever the manager chooses to play he can trust us to do well. That is the secret to having a successful squad.
"We have got such a good, talented group that no matter who comes in and plays we are confident we can win all of our games.
"But hopefully I have given the manager some food for thought with my performance in the game against Stenhousemiur at the weekend."
Foster, who returned to Rangers for a second spell this summer after being released by Bristol City, has spent seven weeks out of action this season.
He suffered a serious ankle injury after a bad challenge by Callum Morris in the League One showdown with second-placed Dunfermline.
The former Aberdeen ace, who enjoyed a highly-successful loan spell at Ibrox in the 2010/11 campaign, made his comeback last week.
He came on as a substitute against, ironically enough, Dunfermline at East End Park on Monday towards the end of an emphatic and important 4-0 victory.
And he also came off the bench late on in the narrow 1-0 triumph over bottom-placed Airdrie at the Excelsior Stadium on Thursday.
Those brief run outs, together with the 90 minutes he played against Stenhousemuir, have given him the confidence to believe he is fully over his injury problems.
Foster said: "The ankle feels great. Obviously, playing on the artificial surface at Ochilview at the weekend was a big test for it. But I hardly felt the ankle at all.
"I must admit that I felt a bit leggy towards the end of the game. But I hadn't started a game in something like eight weeks so I suppose that has to be expected.
"In that respect, it was a tough run-out at the weekend. But it went well and there have been no problems arising out of the game since then.
"I think all of the players would prefer to play on grass as it is that bit more forgiving than the artificial surfaces. But the game on Sunday was absolutely fine.
"The joints are a bit sore the next day and the day after that. The Ochilview pitch is definitely that bit harder than some of the other ones.
"But that is life in this division and you just need to get on with it and do the job that you are paid to do."
Foster played in both the Champions League - including against Manchester United at Ibrox - and the Europa League during his previous spell at Rangers three years ago.
And he remains totally focused on helping Rangers back to that level.
Foster said: "We are 17 points ahead now after our win over Stenhousemuir at the weekend and are in a strong position.
"We are all enjoying our football and looking forward to every match as it comes along. I have been out for a while and am hoping I can be involved regularly between now and the end of the season."